Sven Ove Samuelsen

• Shala, Nita Kaupang; Veierød, Marit Bragelien; Babigumira, Ronnie; Berge, Leon Alexander Mclaren; Samuelsen, Sven Ove & Kirkeleit, Jorunn [Show all 14 contributors for this article] (2025). Occupational exposures and kidney cancer among 25 000 male offshore petroleum industry workers: relative risks and healthy worker survivor bias. American Journal of Epidemiology. ISSN 0002-9262. 195(1), p. 81–91. doi: 10.1093/aje/kwaf039. Full text in Research Archive Show summary

  Kidney cancer has been a suspected occupational disease in petroleum workers. Health conditions that are linked to kidney cancer may prompt termination or change of work, and thereby restrict occupational exposures in high-risk individuals, creating a healthy worker survivor bias (HWSB). We examined associations between occupational exposures and kidney cancer among males in the Norwegian Offshore Petroleum Workers (NOPW) cohort using a case-cohort design, with 169 incident cancers identified by linkage to national registry data (1999-2021) and a subcohort of 2090 non-cases, all employed 1965-1998. Relative risks (hazard ratios, HRs) by cumulative exposure to benzene, crude oil, chlorinated degreasing agents (CDA), asbestos, welding fumes, or surface treatment (priming, painting), were estimated by weighted Cox regression. Inverse exposure-response trends suggested HWSB, reinforced by analyses of necessary components of HWSB. Bias was partly alleviated by adjustment for total employment duration, and by 20-year lagging of cumulative exposure to benzene, crude oil, or CDA. Workers in surface treatment (ever vs. never) showed increased HR=2.22, 95% confidence interval 1.04-4.72 (9 cases, only). For asbestos and welding fumes, the initial inverse trends largely remained after adjustment. In sum, we could neither confirm nor exclude an occupational impact on kidney cancer.

• Babigumira, Ronnie; Veierød, Marit Bragelien; Larsen, Inger Kristin; Berge, Leon Alexander Mclaren; Shala, Nita Kaupang & Marjerrison, Niki [Show all 22 contributors for this article] (2025). Benzene exposure and risk of colorectal cancer by anatomical subsite in the Norwegian offshore petroleum workers cohort. Environmental Research. ISSN 0013-9351. 276, p. 1–9. doi: 10.1016/j.envres.2025.121407. Full text in Research Archive Show summary

  Objective: To investigate the association between low levels of benzene exposure (≤0.879 parts per million [ppm]-years) and risk of colorectal cancer (CRC) including its anatomical subsites. Methods: Among 25,347 male workers in the Norwegian Offshore Petroleum Workers (NOPW) cohort with offshore work history (1965–1998), 455 CRC cases were diagnosed 1999–2021. We compared these with a subcohort (n = 2031) drawn from the full cohort. Work histories were linked to a previously developed industry-specific benzene job-exposure matrix (JEM). Cox regression for case-cohort analyses was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for CRC, adjusted for age, body mass index, smoking, alcohol intake, red/processed meat intake, and physical activity. Results: Risks of CRC increased with increasing benzene exposure. For all CRC, the HRs (95% CI) for the most exposed [quartile 4] vs. the unexposed were 1.32 (0.96 to 1.81, [0.177–0.879 ppm-years]; p-trend = 0.085) for cumulative, 1.52 (1.11 to 2.07, [17–34 years]; p-trend = 0.032) for duration, and 1.56 (1.15 to 2.12, [0.015–0.046 ppm]; p-trend = 0.005) for average intensity of benzene exposure. For right-sided colon cancer, the association was most evident for exposure duration (HR = 2.25 (1.33 to 3.80), quartile 4 [17–34 years] vs. unexposed; p-trend = 0.007). Sensitivity analyses showed consistent associations. Conclusion: This study found positive exposure-response associations between low-level benzene exposure and CRC risk in offshore petroleum workers. These findings add to emerging evidence that benzene can be associated with solid tumours including lung and bladder, which potentially has important occupational and public health implications.

• Aga, Ruth; Søgaard, Anne-Johanne; Holvik, Kristin; Hagen, Terje P.; Idland, Gro & Jeyananthan, Anita [Show all 10 contributors for this article] (2025). Effectiveness of a fall and fracture prevention pathway on hip fracture risk, need of permanent care and mortality: a controlled before-and-after study. Age and Ageing. ISSN 0002-0729. 54(6). doi: 10.1093/ageing/afaf161. Full text in Research Archive Show summary

  Background The high rates of hip fracture in Oslo inspired a new fall prevention pathway based on well-established fall prevention strategies, but specifically focusing on care coordination, osteoporosis treatment and targeting high-risk patients. Objective To evaluate the effectiveness of the fall prevention pathway. Methods We performed a controlled before-and-after study in the home-dwelling population aged 65+ years in Oslo, Norway. The intervention consisted of identifying older adults with a fall-related injury, offering them risk assessment and tailored interventions. Using registry data, we compared registered fallers in the two intervention boroughs with the remaining 13 boroughs as controls, with registered fall injuries as time-dependent exposure in Cox regression. Hazard ratios (HRs) for later hip fracture, long-term care and all-cause mortality were estimated, adjusting for the pre-intervention period. Results The risk of hip fracture for the Oslo population aged 65+ years declined by 23% from 2012–19. HR for hip fracture amongst registered fallers in the intervention boroughs compared to the controls was 0.95 (95% CI 0.64–1.41). The difference was significant in men only [HR 0.45 (95% CI 0.21–0.95)]. The risk of admittance to long-term care was reduced [HR 0.76 (95% CI 0.62–0.93)]. No significant difference was seen in mortality. Conclusions Overall, the risk of later hip fracture was not significantly reduced in all registered fallers in the intervention boroughs, only in men. There was a significant decline in risk of admission to nursing homes in the intervention boroughs. These results suggest that the prevention pathway might have slowed down functional decline in the older Oslo population.

• Berge, Leon Alexander Mclaren; Shala, Nita Kaupang; Barone-Adesi, Francesco; Hosgood, H Dean; Samuelsen, Sven Ove & Bråtveit, Magne [Show all 13 contributors for this article] (2024). Exposure to fibres and risk of pleural mesothelioma in the Norwegian Offshore Petroleum Workers cohort. Occupational and Environmental Medicine. ISSN 1351-0711. 81(7), p. 331–338. doi: 10.1136/oemed-2024-109424. Full text in Research Archive Show summary

  Objectives Pleural mesothelioma is a rare respiratory cancer, mainly caused by inhalation of asbestos fibres. Other inorganic fibres are also suggested risk factors. We aimed to investigate the association between exposure to asbestos or refractory ceramic fibres (RCFs) and pleural mesothelioma among male Norwegian offshore petroleum workers. Methods Among 25 347 men in the Norwegian Offshore Petroleum Workers (NOPW) cohort (1965–1998), 43 pleural mesothelioma cases were identified through the Cancer Registry of Norway (1999–2022). A case–cohort study was conducted with 2095 randomly drawn non-cases from the cohort. Asbestos and RCF exposures were assessed with expert-made job-exposure matrices (JEMs). Weighted Cox regression was used to estimate HRs and 95% CIs, adjusted for age at baseline and pre-offshore employment with likely asbestos exposure. Results An increased risk of pleural mesothelioma was indicated for the highest versus lowest tertile of average intensity of asbestos (HR=1.21, 95% CI: 0.57 to

• Holvik, Kristin; Dahl, Cecilie; Samuelsen, Sven Ove; Søgaard, Anne-Johanne; Solbakken, Siri Marie & Tell, Grethe Seppola [Show all 14 contributors for this article] (2024). Educational gradient in hip fracture incidence in Norway. The Norwegian Epidemiologic Osteoporosis Studies (NOREPOS). Osteoporosis International. ISSN 0937-941X. 35, p. 2047–2053. doi: 10.1007/s00198-024-07133-1. Full text in Research Archive Show summary

  Summary: Examining fracture dynamics by socioeconomic status may inform healthcare and prevention. We found a higher risk of hip fracture in men and women with lower educational level in Norway. However, by age 90 + years, the cumulative incidence was higher in those with higher education, due to their higher life expectancy. Purpose: Socioeconomic gradients are seen for several health outcomes in high-income countries. We aimed to examine possible educational gradients in risk of hip fracture in Norway and to describe the cumulative incidence of hip fracture by educational level. Methods: In a population-wide cohort of Norwegians aged ≥ 50 years, information on attained education from Statistics Norway was linked to hospital-treated hip fractures and deaths during 2002–2019. We estimated relative fracture risk by educational level (primary, secondary or tertiary) in Cox proportional hazards regression. We also examined the cumulative incidence over attained age by gender and educational level in competing risk regression. Results: The population included N = 1,389,858 individuals with 135,938 incident hip fractures. Compared with men who had attained tertiary education, hazard ratios (95% confidence intervals) for hip fracture were 1.44 (1.40, 1.49) in men with primary education only and 1.26 (1.22, 1.29) in men with secondary education. In women, the corresponding estimates were 1.28 (1.25, 1.31) and 1.16 (1.13, 1.19). In the age range 50 to 90 years, the highest cumulative incidence of hip fracture was seen in those with primary education. The gradient gradually diminished with advancing age and was reversed in the oldest (> 90 years) in both genders. Conclusions: There was a clear educational gradient in hip fracture incidence in both men and women in Norway, with a higher risk in people with lower education. Despite this, the cumulative incidence of hip fracture in old age was highest among people with higher education, due to their higher life expectancy.

• Shala, Nita Kaupang; Stenehjem, Jo; Babigumira, Ronnie; Liu, Fei-Chih; Berge, Leon Alexander Mclaren & Silverman, Debra T. [Show all 16 contributors for this article] (2023). Exposure to benzene and other hydrocarbons and risk of bladder cancer among male offshore petroleum workers. British Journal of Cancer. ISSN 0007-0920. 129(5), p. 838–851. doi: 10.1038/s41416-023-02357-0. Full text in Research Archive Show summary

  Background Occupational exposures constitute the second leading cause of urinary bladder cancer after tobacco smoking. Increased risks have been found in the petroleum industry, but high-quality exposure data are needed to explain these observations. Methods Using a prospective case-cohort design, we analysed 189 bladder cancer cases (1999–2017) and 2065 randomly drawn non-cases from the Norwegian Offshore Petroleum Workers cohort. Cases were identified in the Cancer Registry of Norway, while work histories (1965–1998) and lifestyle factors were recorded by questionnaire at baseline (1998). Occupational petroleum-related hydrocarbon exposures were assessed by expert-developed job-exposure matrices. Hazard ratios were estimated by weighted Cox-regressions, adjusted for age, tobacco smoking, education, and year of first employment, and with lagged exposures. Results Increased risks were found in benzene-exposed workers, either long-term exposure (≥18.8 years, HR = 1.89, 95% CI: 1.14–3.13; p-trend = 0.044) or high-level cumulative benzene exposure (HR = 1.60, 95% CI: 0.97–2.63; p-trend = 0.065), compared with the unexposed. Associations persisted with 20-year exposure lag. No associations were found with skin or inhalation exposure to crude oil, mineral oil (lubrication, hydraulics, turbines, drilling), or diesel exhaust. Conclusions The results suggest that exposures in the benzene fraction of the petroleum stream may be associated with increased bladder cancer risk.

• Babigumira, Ronnie; Veierød, Marit Bragelien; Hosgood, H. Dean; Samuelsen, Sven Ove; Bråtveit, Magne & Kirkeleit, Jorunn [Show all 13 contributors for this article] (2023). Benzene exposure and risk of lung cancer in the Norwegian Offshore Petroleum Worker cohort: a prospective case-cohort study. Occupational and Environmental Medicine. ISSN 1351-0711. 81(1). doi: 10.1136/oemed-2023-109139. Full text in Research Archive Show summary

  Objective The objective of our study was to examine whether occupational exposure to benzene is associated with lung cancer among males in the Norwegian Offshore Petroleum Workers cohort. Methods Among 25 347 male offshore workers employed during 1965–1998, we conducted a case-cohort study with 399 lung cancer cases diagnosed between 1999 and 2021, and 2035 non-cases sampled randomly by 5-year birth cohorts. Individual work histories were coupled to study-specific job-exposure matrices for benzene and other known lung carcinogens. Weighted Cox regression was used to estimate HRs and 95% CIs for the associations between benzene exposure and lung cancer, by major histological subtypes, adjusted for age, smoking and occupational exposure to welding fumes, asbestos and crystalline silica. Missing data were imputed. Results For lung cancer (all subtypes combined), HRs (95% CIs) for the highest quartiles of benzene exposure versus unexposed were 1.15 (0.61 to 2.35) for cumulative exposure, 1.43 (0.76 to 2.69) for duration, and 1.22 (0.68 to 2.18) for average intensity (0.280≤P-trend≤0.741). For 152 adenocarcinoma cases, a positive trend was observed for exposure duration (P-trend=0.044). Conclusions In this cohort of offshore petroleum workers generally exposed to low average levels of benzene, we did not find an overall clear support for an association with lung cancer (all subtypes combined), although an association was suggested for duration of benzene exposure and adenocarcinoma. The limited evidence might be due to restricted statistical power.

• Fischer, Nantje; Træen, Bente & Samuelsen, Sven Ove (2022). Sexual Debut Ages in Heterosexual Norwegians Across Six Birth Cohorts. Sexuality & Culture. ISSN 1095-5143. doi: 10.1007/s12119-022-10045-z. Full text in Research Archive Show summary

  This study aims to estimate six different sexual debut ages in heterosexual Norwegians in six birth cohorts of the general population in Norway. The results are based on a 2020 national web panel survey of 18–89-year-olds in Norway (n = 4160). There was a general decline in the median debut age from those aged 70+ to those 18–29 (born 1991–2002). Oral sex with a female partner has become increasingly common among men at an earlier age across generations. The same pattern was found in women as well with regard to oral sex with a male partner and receptive anal sex. There was a slight increase in median debut age in 18–29-year-olds for receptive vaginal sex (born 1991–2002). The median debut age for vaginal sex was fairly stable for generations of men and women born after 1950.

• Liu, Fei-Chih; Veierød, Marit Bragelien; Kjærheim, Kristina; Robsahm, Trude Eid; Ghiasvand, Reza & Hosgood, H Dean [Show all 17 contributors for this article] (2022). Night shift work, chemical coexposures and risk of female breast cancer in the Norwegian Offshore Petroleum Workers (NOPW) cohort: A prospectively recruited case-cohort study. BMJ Open. 12(1). doi: 10.1136/bmjopen-2021-056396. Full text in Research Archive Show summary

  Objectives This study examined the association between night shift work and risk of breast cancer, overall and by hormone receptor subtype, among females in the Norwegian Offshore Petroleum Workers (NOPW) cohort. We also examined the association of coexposure (chlorinated degreasers and benzene) and breast cancer risk, and possible interaction with work schedule. Design Prospectively recruited case- cohort study within the NOPW cohort. Setting Female offshore petroleum workers active on the Norwegian continental shelf. Participants 600 female workers (86 cases and 514 non- cases) were included in the study. We excluded workers that died or emigrated before start of follow-up, had missing work history, were diagnosed with breast cancer or other prior malignancy (except non-melanoma skin cancer) before start of follow-up. Results No overall association was found between breast cancer risk and work schedule (HR 0.87, 95% CI 0.52 to 1.46 for work schedule involving night shift vs day shift only). There was no significant association between work schedule and risk of any breast cancer subtype. No significant interactions were found between work schedule and chemical coexposures (breast cancer overall Pinteraction chlorinated degreasers =0.725 and Pinteraction benzene =0.175). Conclusions Our results did not provide supporting evidence that work schedule involving night shift affects breast cancer risk in female offshore petroleum workers, but should be considered cautiously due to few cases. Further studies with larger sample sizes are warranted

• Berge, Leon Alexander Mclaren; Liu, Fei-Chih; Grimsrud, Tom Kristian; Babigumira, Ronnie; Støer, Nathalie Charlotte & Kjærheim, Kristina [Show all 15 contributors for this article] (2022). Night shift work and risk of aggressive prostate cancer in the Norwegian Offshore Petroleum Workers (NOPW) cohort. International Journal of Epidemiology. ISSN 0300-5771. 52(4), p. 1003–1014. doi: 10.1093/ije/dyac235. Full text in Research Archive Show summary

  Background: Night shift work may acutely disrupt the circadian rhythm, with possible carcinogenic effects. Prostate cancer has few established risk factors though night shift work, a probable human carcinogen, may increase the risk. We aimed to study the association between night shift work and chlorinated degreasing agents (CDAs) as possible endocrine disrupters in relation to aggressive prostate cancer as verified malignancies. Methods: We conducted a case-cohort study on 299 aggressive prostate cancer cases and 2056 randomly drawn non-cases in the Norwegian Offshore Petroleum Workers cohort (1965-98) with linkage to the Cancer Registry of Norway (1953-2019). Work history was recorded as years with day, night, and rollover (rotating) shift work, and CDA exposure was assessed with expert-made job-exposure matrices. Weighted Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for aggressive prostate cancer, adjusted for education and year of first employment, stratified by 10-year birth cohorts, and with 10, 15, and 20 years of exposure lag periods. Results: Compared with day work only, an increased hazard of aggressive prostate cancer (HR = 1.86, 95% CI 1.18-2.91; P-trend = 0.046) was found in workers exposed to ≥19.5 years of rollover shift work. This persisted with longer lag periods (HR = 1.90, 95% CI 0.92-3.95; P-trend = 0.007). The exposure-hazard curve for a non-linear model increased linearly (HRs ≥1.00) for 18-26 years of rollover shift work. No association was found with CDA exposure. Conclusions: Long-term exposure to rollover shift work may increase the hazard of aggressive prostate cancer in offshore petroleum workers.

• Bekkhus, Mona; Lee, Yunsung; Samuelsen, Sven Ove; Tsotsi, Stella & Magnus, Per Minor (2022). Maternal and paternal anxiety during pregnancy: Comparing the effects on behavioral problems in offspring. PLOS ONE. 17(10). doi: 10.1371/journal.pone.0275085. Full text in Research Archive Show summary

  Prenatal maternal anxiety has been associated with both short and long-term mental health problems in the child. The current study aims to examine the association between maternal and paternal prenatal anxiety and behaviour problems in the child at 1.5 and 5 years, using three different approaches; (1) adjusting for covariates, (2) using fathers’ anxiety during pregnancy as a negative control, and (3) using a sibling-comparison design, controlling for unmeasured family factors. We used data from the Norwegian Mother, Father and Child Cohort Study (MoBa) is used. MoBa is a cohort consisting of about 114 000 pregnancies (about 34000 siblings) recruited from 1999 to 2008. Self-reported measures on maternal anxiety were obtained twice in pregnancy and 6 months after birth, while paternal anxiety was reported prenatally at 17 th weeks of gestation. Maternal reports on child behaviour problems were obtained at 1.5 and 5 years of age. Results suggests that prenatal exposure to maternal anxiety was associated with behaviour problems at 1.5 years: adjusted beta (β) = 0.13 (CI = 0.12, 0.15), and at 5 years: β = 0.11 (CI = 0.09, 0.14). However, paternal anxiety was also associated with behaviour problems at 1.5 years: β = 0.03 (CI = 0.01–0.03) and at 5 years β = 0.03 (CI = 0.02, 0.03). These associations were attenuated in the sibling comparison analyses: β = - 0.02 (CI = -0.02–0.05) at 1.5 years and β = -0.05 (CI = -0.10, 0.02) at 5 years. In conclusions, the sibling analyses are not consistent with a direct effect of prenatal maternal anxiety on child behaviour problems. It is more likely that genetic or shared family environment explain this association.

• Samuelsen, Sven Ove (2022). Cox regression can be collapsible and Aalen regression can be non-collapsible. Lifetime Data Analysis. ISSN 1380-7870. doi: 10.1007/s10985-022-09578-0. Full text in Research Archive Show summary

  Abstract It is well-known that the additive hazards model is collapsible, in the sense that when omitting one covariate from a model with two independent covariates, the marginal model is still an additive hazards model with the same regression coefficient or function for the remaining covariate. In contrast, for the proportional hazards model under the same covariate assumption, the marginal model is no longer a proportional hazards model and is not collapsible. These results, however, relate to the model specification and not to the regression parameter estimators. We point out that if covariates in risk sets at all event times are independent then both Cox and Aalen regression estimators are collapsible, in the sense that the parameter estimators in the full and marginal models are consistent for the same value. Vice-versa, if this assumption fails, then the estimates will change systematically both for Cox and Aalen regression. In particular, if the data are generated by an Aalen model with censoring independent of covariates both Cox and Aalen regression is collapsible, but if generated by a proportional hazards model neither estimators are. We will also discuss settings where survival times are generated by proportional hazards models with censoring patterns providing uncorrelated covariates and hence collapsible Cox and Aalen regression estimates. Furthermore, possible consequences for instrumental variable analyses are discussed.

• Lawrence, Graeme; Midtervoll, Ingvild K.; Samuelsen, Sven Ove; Kristoffersen, Anne Karin; Enersen, Morten & Håheim, Lise Lund (2022). The blood microbiome and its association to cardiovascular disease mortality: case-cohort study. BMC Cardiovascular Disorders. 22(1). doi: 10.1186/s12872-022-02791-7. Full text in Research Archive Show summary

  Background Little is known about the association between bacterial DNA in human blood and the risk of cardiovascular disease (CVD) mortality. Methods A case-cohort study was performed based on a 9 ½ year follow-up of the Oslo II study from 2000. Eligible for this analysis were men born in 1923 and from 1926 to 1932. The cases were men (n = 227) who had died from CVD, and the controls were randomly selected participants from the same cohort (n = 178). Analysis of the bacterial microbiome was performed on stored frozen blood samples for both cases and controls. Association analyses for CVD mortality were performed by Cox proportional hazard regression adapted to the case-cohort design. We used the Bonferroni correction due to the many bacterial genera that were identified. Results Bacterial DNA was identified in 372 (82%) of the blood samples and included 78 bacterial genera from six phyla. Three genera were significantly associated with CVD mortality. The genera Kocuria (adjusted hazard ratio (HR) 8.50, 95% confidence interval (CI) (4.05, 17.84)) and Enhydrobacter (HR 3.30 (2.01, 5.57)) indicate an association with CVD mortality with increasing levels. The genera Paracoccus (HR 0.29 (0.15, 0.57)) was inversely related. Significant predictors of CVD mortality were: the feeling of bad health; and the consumption of more than three cups of coffee per day. The following registered factors were borderline significant, namely: a history of heart failure; increased systolic blood pressure; and currently taking antihypertensive drugs now, versus previously. Conclusions The increasing levels of two bacterial genera Kocuria (skin and oral) and Enhydrobacter (skin) and low levels of Paracoccus (soil) were associated with CVD mortality independent of known risk factors for CVD.

• Bekkhus, Mona; Lee, Yunsung; Brandlistuen, Ragnhild Eek; Samuelsen, Sven Ove & Magnus, Per Minor (2021). Maternal Anxiety and Infants Birthweight and Length of Gestation. A sibling design. BMC Psychiatry. 21. doi: 10.1186/s12888-021-03620-5. Full text in Research Archive Show summary

  Background The overall aim of this study is to examine the effect of prenatal maternal anxiety on birthweight and gestational age, controlling for shared family confounding using a sibling comparison design. Methods The data on 77,970 mothers and their 91,165 children from the population-based Mother, Father and Child Cohort Study and data on 12,480 pairs of siblings were used in this study. The mothers filled out questionnaires for each unique pregnancy, at 17th and 30th week in pregnancy. Gestational age and birth weight was extracted from the Medical Birth Registry of Norway (MBRN). Associations between prenatal maternal anxiety (measured across the 17th and 30th weeks) and birth outcomes (birthweight and gestational age) were examined using linear regression with adjustment for shared-family confounding in a sibling comparison design. Results In the population level analysis the maternal anxiety score during pregnancy was inversely associated with new-born’s birthweight (Beta = -63.8 95% CI: -92.6, -35.0) and gestational age (Beta = -1.52, 95% CI: -2.15, -0.89) after adjustment for several covariates. The association of the maternal anxiety score with birthweight was no longer significant, but remained for maternal anxiety at 30th week with gestational age (Beta = -1.11, 95% CI: -1.82, -0.4) after further adjusting for the shared-family confounding in the sibling comparison design. Conclusion No association was found for maternal prenatal anxiety with birth weight after multiple covariates and family environment were controlled. However, there was an association between prenatal maternal anxiety at 30th week only with gestational age, suggesting a timing effect for maternal anxiety in third trimester.

• Gunnes, Nina; Gjessing, Håkon K.; Bakken, Inger Johanne Landsjøåsen; Ghaderi, Sara; Gran, Jon Michael & Hungnes, Olav [Show all 13 contributors for this article] (2020). Seasonal and pandemic influenza during pregnancy and risk of fetal death: A Norwegian registry‑based cohort study. European Journal of Epidemiology (EJE). ISSN 0393-2990. 35, p. 371–379. doi: 10.1007/s10654-020-00600-z. Full text in Research Archive Show summary

  Previous studies of fetal death with maternal influenza have been inconsistent. We explored the effect of maternal influenza-like illness (ILI) in pregnancy on the risk of fetal death, distinguishing between diagnoses during regular influenza seasons and the 2009/2010 pandemic and between trimesters of ILI. We used birth records from the Medical Birth Registry of Norway to identify fetal deaths after the first trimester in singleton pregnancies (2006–2013). The Norwegian Directorate of Health provided dates of clinical influenza diagnoses by primary-health-care providers, whereas dates of laboratory-confirmed influenza A (H1N1) diagnoses were provided by the Norwegian Surveillance System for Communicable Diseases. We obtained dates and types of influenza vaccinations from the Norwegian Immunisation Registry. Cox proportional-hazards regression models were fitted to estimate hazard ratios (HRs) of fetal death, with associated 95% confidence intervals (CIs), comparing women with and without an ILI diagnosis in pregnancy. There were 2510 fetal deaths among 417,406 eligible pregnancies. ILI during regular seasons was not associated with increased risk of fetal death: adjusted HR = 0.90 (95% CI 0.64–1.27). In contrast, ILI during the pandemic was associated with substantially increased risk of fetal death, with an adjusted HR of 1.75 (95% CI 1.21–2.54). The risk was highest following first-trimester ILI (adjusted HR = 2.28 [95% CI 1.45–3.59]). ILI during the pandemic—but not during regular seasons—was associated with increased risk of fetal death in the second and third trimester. The estimated effect was strongest with ILI in first trimester.

• Rossow, Ingeborg Margrete; Amundsen, Ellen Johanna & Samuelsen, Sven Ove (2020). Socio‐economic differences in all‐cause mortality in people with alcohol use disorder: a prospective cohort study. Addiction. ISSN 0965-2140. 116(1), p. 53–59. doi: 10.1111/add.15070. Full text in Research Archive
• Stoltenberg, Emil Aas; Nordeng, Hedvig Marie Egeland; Ystrøm, Eivind & Samuelsen, Sven Ove (2020). The cure model in perinatal epidemiology. Statistical Methods in Medical Research. ISSN 0962-2802. 29(10), p. 2783–2794. doi: 10.1177/0962280220904092. Full text in Research Archive Show summary

  In the statistical literature, the class of survival analysis models known as cure models has received much attention in recent years. Cure models seem not, however, to be part of the statistical toolbox of perinatal epidemiologists. In this paper, we demonstrate that in perinatal epidemiological studies where one investigates the relation between a gestational exposure and a condition that can only be ascertained after several years, cure models may provide the correct statistical framework. The reason for this is that the hypotheses being tested often concern an unobservable outcome that, in view of the hypothesis, should be thought of as occurring at birth, even though it is only detectable much later in life. The outcome of interest can therefore be viewed as a censored binary variable. We illustrate our argument with a simple cure model analysis of the possible relation between gestational exposure to paracetamol and attention-deficit hyperactivity disorder, using data from the Norwegian Mother, Father and Child Cohort Study conducted by the Norwegian Institute of Public Health, and information about the attention-deficit hyperactivity disorder diagnoses obtained from the Norwegian Patient Registry.

• Stenehjem, Jo S.; Babigumira, Ronnie; Hosgood, H Dean; Veierød, Marit Bragelien; Samuelsen, Sven Ove & Bråtveit, Magne [Show all 18 contributors for this article] (2020). Cohort Profile: The Norwegian Offshore Petroleum Workers (NOPW) Cohort. International Journal of Epidemiology. ISSN 0300-5771. 50(2). doi: 10.1093/ije/dyaa107. Full text in Research Archive
• Hjellvik, Vidar; Bruin, Marie L. de; Samuelsen, Sven Ove; Karlstad, Øystein; Andersen, Morten & Haukka, Jari [Show all 9 contributors for this article] (2019). Adjusting for unmeasured confounding using validation data: Simplified two-stage calibration for survival and dichotomous outcomes. Statistics in Medicine. ISSN 0277-6715. doi: 10.1002/sim.8131. Full text in Research Archive
• Samuelsen, Sven Ove & Støer, Nathalie Charlotte (2018). Inverse Probability Weighting in Nested Case-Control Studies. In Borgan, Ørnulf; Breslow, Norman E.; Chatterjee, Nilanjan; Gail, Mitchell H.; Scott, Alastair & Wild, Christopher J. (Ed.), Handbook of Statistical Methods for Case-Control Studies. CRC Press. ISSN 9781498768580. p. 351–371. doi: 10.1002/sim.6019. Full text in Research Archive
• Borgan, Ørnulf & Samuelsen, Sven Ove (2018). Cohort Sampling for Time-to-Event Data: An Overview. In Borgan, Ørnulf; Breslow, Norman E.; Chatterjee, Nilanjan; Gail, Mitchell H.; Scott, Alastair & Wild, Christopher J. (Ed.), Handbook of Statistical Methods for Case-Control Studies. CRC Press. ISSN 9781498768580. p. 285–301. Full text in Research Archive
• Bekkhus, Mona; Lee, Yunsung; Nordhagen, Rannveig; Magnus, Per; Samuelsen, Sven Ove & Borge, Anne Inger Helmen (2018). Re-examining the link between prenatal maternal anxiety and child emotional difficulties, using a sibling design. International Journal of Epidemiology. ISSN 0300-5771. 47(1), p. 156–165. doi: 10.1093/ije/dyx186. Full text in Research Archive Show summary

  Background: Prenatal exposure to maternal anxiety has been associated with child emotional difficulties in a number of epidemiological studies. One key concern, however, is that this link is vulnerable to confounding by pleiotropic genes or environmental family factors. Methods: Data on 82 383 mothers and children from the population-based Mother and Child Cohort Study and data on 21 980 siblings were used in this study. Mothers filled out questionnaires for each unique pregnancy, for infant difficulties at 6 months and for emotional difficulties at 36 months. The link between prenatal maternal anxiety and child difficulties were examined using logistic regression analyses and multiple linear regression analyses for the full study sample and the sibling sample. Results: In the conventional full-cohort analyses, prenatal exposure to maternal anxiety was associated with child difficulties at both 6 months [odds ratio (OR) = 2.1 (1.94–2.27)] and 36 months [OR = 2.72 (2.47–2.99)]. The findings were essentially the same whether we examined difficulties at 6 months or at 36 months. However, these associations were no longer present once we controlled for potential social and genetic confounders in the sibling comparison analyses, either at 6 months [OR = 1.32 (0.91–1.90)] or at 36 months [OR = 1.28 (0.63–2.60)]. Findings from multiple regression analyses with continuous measures were essentially the same. Conclusions: Our finding lends little support for there being an independent prenatal effect on child emotional difficulties; rather, our findings suggest that the link between prenatal maternal anxiety and child difficulties could be confounded by pleiotropic genes or environmental family factors.

• Stenehjem, Jo Steinson; Robsahm, Trude Eid; Bråtveit, Magne; Samuelsen, Sven Ove; Kirkeleit, Jorunn & Grimsrud, Tom Kristian (2017). Aromatic hydrocarbons and risk of skin cancer by anatomical site in 25 000 male offshore petroleum workers. American Journal of Industrial Medicine. ISSN 0271-3586. 60(8), p. 679–688. doi: 10.1002/ajim.22741. Full text in Research Archive Show summary

  Background: We prospectively examined skin cancer risk according to occupational exposure to aromatic hydrocarbons with adjustment for ultraviolet radiation exposure, in a cohort of 24 917 male offshore petroleum workers. Methods: Hazard ratios (HRs) and 95% confidence intervals were estimated with Cox regression adapted to a stratified case‐cohort design. Results: During 13.5 years of follow‐up, 112 cutaneous melanomas (CMs) and 70 non‐melanoma skin cancers were identified. Increased risks of CM and of squamous cell carcinoma on the forearm and hand were seen among those ever exposed to crude oil or benzene. For skin cancers of the forearm and hand combined, cumulative and duration metrics of benzene exposure showed Ptrends of 0.031 and 0.003, respectively. Conclusions: Our results support an association between exposure to crude oil or benzene and skin cancer risk on hands and forearms among offshore petroleum workers. Dermal uptake of polycyclic aromatic hydrocarbons or benzene may explain this association. This research has been published in the American Journal of Industrial Medicine. © 2017 Wiley

• Stenehjem, Jo Steinson; Robsahm, Trude Eid; Bråtveit, Magne; Samuelsen, Sven Ove; Kirkeleit, Jorunn & Grimsrud, Tom Kristian (2017). Ultraviolet radiation and skin cancer risk in offshore workers. Occupational Medicine. ISSN 0962-7480. 67(7), p. 569–573. doi: 10.1093/occmed/kqx110. Full text in Research Archive Show summary

  Background: Excess skin cancer mortality and incidence have been reported among both land-based and offshore petroleum workers. The association between skin cancer and ultraviolet radiation (UVR) exposure has not been examined in these workers, although they have long off-duty periods and high average income that may allow travelling to sunny destinations. In addition, they have access to solariums free of charge on many accommodation platforms. Aims: To prospectively examine risk of incident cutaneous melanoma (CM) and non-melanoma skin cancer (NMSC), according to sun-tanning habits with adjustment for aromatic hydrocarbon exposure. Methods: A cohort of men employed offshore from 1965 to 1999 was linked through the Cancer Registry of Norway 1999–2012. Cox regression adapted to a stratified case-cohort design was used to estimate hazard ratios with 95% confidence intervals. Results: The cohort included 24917 men. During 13.5 years of follow-up, 112 CMs and 70 NMSCs occurred. A positive dose–response relationship was seen between sunburn frequency and risk of CM (Ptrend < 0.05) and NMSC (Ptrend < 0.01). Solarium use both before and after age 20 was related to increased risk of NMSC. Sunscreen use was associated with increased risk of NMSC (Ptrend < 0.001). Conclusions: UVR exposure seems to be a significant contributor to the elevated risk of skin cancer observed in North Sea offshore workers. The positive association between solarium use and NMSC risk adds to the growing body of literature on artificial UV devices as carcinogenic. This research has been published in Occupational Medicine. © 2017 Oxford University Press

• Træen, Bente; Samuelsen, Sven Ove & Roen, Katrina (2016). Sexual Debut Ages in Heterosexual, Lesbian, Gay, and Bisexual Young Adults in Norway. Sexuality & Culture. ISSN 1095-5143. p. 1–18. doi: 10.1007/s12119-016-9353-2. Full text in Research Archive Show summary

  This study estimates sexual debut ages in young heterosexual, lesbian, gay, and bisexual men and women in Norway. A questionnaire survey was completed online by 27.2 % of a representative national web sample of 2,090 persons aged 18–29 years. Three self-selected samples of 924 respondents completed an extended version of the survey online. Lesbian and bisexual women reported earlier experience of orgasm through masturbation than heterosexual women (median 13.1 versus 15.2 years), and heterosexual men (median 13.5) reported earlier debut than heterosexual women. There was a statistically significant difference between heterosexual and lesbian and bisexual women’s age at the first experience of receptive vaginal sex (median 16.8 versus 15.4 years). As regards experience of insertive vaginal sex, a significantly higher percentage of heterosexual men than women, and of heterosexual and lesbian and bisexual women, reported experience. It was more common among lesbian and bisexual women than heterosexual women to have had oral sex with another woman, but in neither group did the cumulative percent reach 50% by the age of 29 years and the median could not be estimated. Gay and bisexual men reported earlier receptive anal sex debut than heterosexual men. With regard to insertive anal sex, gay and bisexual men accumulated experience earlier than heterosexual men, and lesbian and bisexual women acquired this experience earlier than heterosexual women. Compared to heterosexuals, LGB persons of both genders engage in more varied sexual activities. Lesbian and gay persons have same-sex experiences at an earlier age than bisexuals.

• Meyer, Haakon E; Støer, Nathalie; Samuelsen, Sven Ove; Blomhoff, Rune; Robsahm, Trude Eid & Brustad, Magritt [Show all 8 contributors for this article] (2016). Long Term Association between Serum 25-Hydroxyvitamin D and Mortality in a Cohort of 4379 Men. PLOS ONE. 11(3). doi: 10.1371/journal.pone.0151441. Full text in Research Archive Show summary

  Objective A number of observational studies have shown an inverse association between circulating 25-hydroxyvitamin D and total mortality, but a reverse J-shaped association has also been reported. In a large nested case-control study, serum-25-hydroxyvitamin D (s-25(OH)D) was positively associated with incident prostate cancer. Based on the same study population, the primary aim of the present study was to investigate the association between s-25 (OH)D and total mortality. Methods Men participating in population based health screenings during 1981–1991 and enrolled in a nested case-control study were followed throughout 2007 with respect to all-cause and cause-specific mortality. Hazard ratios (HR) with 95% confidence intervals (CI) were calculated using Cox proportional hazards regression. Results In men with prostate cancer (n = 2282), there was a significant inverse association between s-25(OH)D and total mortality after controlling for potential confounders (HR = 1.25 (95% CI 1.05–1.50), s-25(OH)D < 50 nmol/l versus s-25(OH)D > 50 nmol/l). The corresponding figure among controls (n = 2147) was HR = 1.15 (95% CI 0.88–1.50) and in the total study.population HR = 1.19 (95% CI 1.03–1.38). For cause-specific deaths, we found no significant associations. Conclusions In this study population, s-25(OH)D was inversely associated with total mortality during more than two decades of follow-up, despite, as previous reported, high s-25(OH)D was associated with increased risk of prostate cancer.

• Støer, Nathalie & Samuelsen, Sven Ove (2016). MultipleNCC: Inverse probability weighting of nested case-control data. The R Journal. 8(2), p. 5–18. doi: 10.32614/rj-2016-030. Full text in Research Archive
• Finnes, Trine Elisabeth; Lofthus, Cathrine Marie; Meyer, Haakon E; Søgaard, Anne-Johanne; Tell, Grethe Seppola & Apalset, Ellen M [Show all 12 contributors for this article] (2016). A combination of low serum concentrations of vitamins K1 and D is associated with increased risk of hip fractures in elderly Norwegians: a NOREPOS study. Osteoporosis International. ISSN 0937-941X. 27(4), p. 1645–1652. doi: 10.1007/s00198-015-3435-0. Full text in Research Archive
• Stenehjem, Jo Steinson; Kjærheim, Kristina; Bråtveit, Magne; Samuelsen, Sven Ove; Barone-Adesi, Francesco & Rothman, Nathaniel [Show all 8 contributors for this article] (2015). Benzene exposure and risk of lymphohaematopoietic cancers in 25 000 offshore oil industry workers. British Journal of Cancer. ISSN 0007-0920. 112(9), p. 1603–1612. doi: 10.1038/bjc.2015.108. Full text in Research Archive Show summary

  Background: The aim of this work was to examine the risk of lymphohaematopoietic (LH) cancer according to benzene exposure among offshore workers. Methods: Cancer registry data were used to identify 112 cancer cases diagnosed during 1999–2011 in a cohort of 24 917 Norwegian men reporting offshore work between 1965 and 1999. Analyses were conducted according to a stratified case–cohort design with a reference subcohort of 1661 workers. Cox regression was used to estimate hazard ratios with 95% confidence intervals, adjusted for other benzene exposure and smoking. Results: Most workers were exposed to benzene for <15 years. The upper range values of average intensity and cumulative exposure were estimated to 0.040 p.p.m. and 0.948 p.p.m.-years, respectively. Risks were consistently elevated among exposed workers for all LH cancers combined and for most subgroups, although case numbers were small and yielded imprecise risk estimates. There was evidence of dose-related risk patterns according to cumulative exposure for acute myeloid leukaemia (AML), multiple myeloma (MM) (P trends 0.052 and 0.024, respectively), and suggestively so for chronic lymphocytic leukaemia (CLL) according to average intensity (P trend 0.094). Conclusions: Our results support an association between cumulative and intensity metrics of low-level benzene exposure and risk for AML, MM, and suggestively for CLL.

• Holvik, Kristin; Ahmed, Luai Awad; Forsmo, Siri; Gjesdal, Clara Gram; Grimnes, Guri & Samuelsen, Sven Ove [Show all 10 contributors for this article] (2015). No increase in risk of hip fracture at high serum retinol concentrations in community-dwelling older Norwegians: the Norwegian Epidemiologic Osteoporosis Studies. American Journal of Clinical Nutrition. ISSN 0002-9165. 102(5), p. 1289–1296. doi: 10.3945/ajcn.115.110528. Full text in Research Archive
• Holvik, Kristin; Gjesdal, Clara Gram; Tell, Grethe Seppola; Grimnes, Guri; Schei, Berit & Apalset, Ellen M [Show all 10 contributors for this article] (2014). Low serum concentrations of alpha-tocopherol are associated with increased risk of hip fracture. A NOREPOS study. Osteoporosis International. ISSN 0937-941X. 25(11), p. 2545–2554. doi: 10.1007/s00198-014-2802-6. Full text in Research Archive
• Finnes, Trine Elisabeth; Lofthus, Cathrine Marie; Meyer, Haakon E.; Eriksen, Erik Fink; Apalset, Ellen M & Tell, Grethe S [Show all 9 contributors for this article] (2014). Procollagen type 1 amino-terminal propeptide (P1NP) and risk of hip fractures in elderly Norwegian men and women. A NOREPOS study. Bone. ISSN 8756-3282. 64, p. 1–7. doi: 10.1016/j.bone.2014.03.010. Full text in Research Archive Show summary

  The current study aimed to assess a possible association between the bone turnover marker procollagen type 1 amino-terminal propeptide (P1NP) and future hip fractures in elderly Norwegian men and women and to elucidate the relation between P1NP, bone mineral density and 25-hydroxyvitamin D (25(OH)D). Men and women aged 71 to 77 from two population based health studies in Norway (1999-2001) were followed for a median period of 7.3years with respect to hip fractures. The study was designed as a case-cohort study. P1NP and 25(OH)D were analysed in frozen serum samples obtained at baseline in hip fracture patients (n=340) and in randomly selected sex stratified sub-cohorts. Bone mineral density was measured by dual-energy X-ray absorptiometry (DXA) in a subset of participants. Cox proportional hazards regression with inverse probability weighting and robust variance was performed. No significant correlation between 25(OH)D and P1NP was found. A negative correlation between P1NP and BMD was observed in women (Rho=-0.36, p=0.001). A similar trend was observed in men. No association between quartiles of P1NP and rate of subsequent hip fractures was found. Spline analyses suggested a higher rate of hip fracture at P1NP levels above 60μg/L in both men and women. A higher hip fracture rate, which was independent of BMD, was also indicated in women with very low levels of P1NP.

• Støer, Nathalie & Samuelsen, Sven Ove (2013). Inverse probability weighting in nested case-control studies with additional matching-a simulation study. Statistics in Medicine. ISSN 0277-6715. 32(30), p. 5328–5339. doi: 10.1002/sim.6019. Full text in Research Archive
• Borgan, Ørnulf & Samuelsen, Sven Ove (2013). Nested Case-Control and Case-Cohort Studies. In Klein, John P; Houwelingen, Hans C van; Ibrahim, Joseph G & Scheike, Thomas H (Ed.), Handbook of Survival Analysis. CRC Press. ISSN 9781466555662. p. 343–367. Full text in Research Archive
• Holvik, Kristin; Ahmed, Luai Awad; Forsmo, Siri; Gjesdal, Clara Gram; Grimnes, Guri & Samuelsen, Sven Ove [Show all 10 contributors for this article] (2013). Low Serum Levels of 25-Hydroxyvitamin D Predict Hip Fracture in the Elderly: A NOREPOS Study. Journal of Clinical Endocrinology and Metabolism (JCEM). ISSN 0021-972X. 98(8), p. 3341–3350. doi: 10.1210/jc.2013-1468. Full text in Research Archive Show summary

  Background: Despite considerable interest, the relationship between circulating 25-hydroxyvitamin D and the risk of hip fracture is not fully established. Objective: The objective of the study was to study the association between serum 25-hydroxyvitamin D concentrations [s-25(OH)D] and the risk of hip fracture in Norway, a high-latitude country that has some of the highest hip fracture rates worldwide. Methods: A total of 21 774 men and women aged 65–79 years attended 4 community-based health studies during 1994–2001. Information on subsequent hip fractures was retrieved from electronic hospital discharge registers, with a maximum follow-up of 10.7 years. Using a stratified case-cohort design, s-25(OH)D was determined by HPLC-atmospheric pressure chemical ionization-mass spectrometry in stored serum samples in hip fracture cases (n = 1175; 307 men, 868 women) and in gender-stratified random samples (n = 1438). Cox proportional hazards regression adapted for the case-cohort design was performed. Results: We observed an inverse association between s-25(OH)D and hip fracture; those with s-25(OH)D in the lowest quartile (<42.2 nmol/L) had a 38% [95% confidence interval (CI) 9–74%] increased risk of hip fracture compared with the highest quartile (≥67.9 nmol/L) in a model accounting for age, gender, study center, and body mass index. The association was stronger in men than in women: hazard ratio 1.65 (95% CI 1.04–2.61) vs hazard ratio 1.25 (95% CI 0.95–1.65). Conclusion: In this prospective case-cohort study of hip fractures, the largest ever reported, we found an increased risk of hip fracture in subjects in the lowest compared with the highest quartile of serum 25-hydroxyvitamin D. In accordance with the findings of previous community-based studies, low vitamin D status was a modest risk factor for hip fracture.

• Vikanes, Åse Vigdis; Støer, Nathalie; Gunnes, Nina; Grjibovski, Andrej; Samuelsen, Sven Ove & Magnus, Per [Show all 7 contributors for this article] (2013). Helicobacter pylori infection and severe hyperemesis gravidarum among immigrant women in Norway: a case–control study. European Journal of Obstetrics, Gynecology, and Reproductive Biology. ISSN 0301-2115. 167(1), p. 41–46. doi: 10.1016/j.ejogrb.2012.11.007. Full text in Research Archive
• Håberg, Siri Eldevik; Trogstad, Lill; Gunnes, Nina; Wilcox, AJ; Gjessing, Håkon K. & Samuelsen, Sven Ove [Show all 19 contributors for this article] (2013). Risk of Fetal Death after Pandemic Influenza Virus Infection or Vaccination. New England Journal of Medicine. ISSN 0028-4793. 368(4), p. 333–340. doi: 10.1056/NEJMoa1207210. Full text in Research Archive
• Haavaldsen, Camilla; Samuelsen, Sven Ove & Eskild, Anne (2013). Fetal death and placental weight/birthweight ratio: a population study. Acta Obstetricia et Gynecologica Scandinavica. ISSN 0001-6349. 92(5), p. 583–590. doi: 10.1111/aogs.12105. Full text in Research Archive
• Samuelsen, Sven Ove & Veierød, Marit Bragelien (2012). Poisson regression. In Veierød, Marit Bragelien; Lydersen, Stian & Laake, Petter (Ed.), Medical statistics in clinical and epidemiological research. Gyldendal Akademisk. ISSN 9788205399594. p. 200–230. Full text in Research Archive
• Gulsvik, Anne Kristine; Thelle, Dag Steinar; Samuelsen, Sven Ove; Myrstad, Marius; Mowe, Morten & Wyller, Torgeir Bruun (2012). Ageing, physical activity and mortality - a 42-year follow-up study. International Journal of Epidemiology. ISSN 0300-5771. 41(2), p. 521–530. doi: 10.1093/ije/dyr205. Full text in Research Archive
• Gjerde, Hallvard; Christophersen, Asbjørg S; Normann, Per Trygve; Pettersen, Bjørg Sjøgren; Sabaredzovic, Azemira & Samuelsen, Sven Ove [Show all 7 contributors for this article] (2012). Analysis of Alcohol and Drugs in Oral Fluid From Truck Drivers in Norway. Traffic Injury Prevention. ISSN 1538-9588. 13(1), p. 43–48. doi: 10.1080/15389588.2011.627957. Full text in Research Archive
• Støer, Nathalie & Samuelsen, Sven Ove (2012). Comparison of estimators in nested case-control studies with multiple outcomes. Lifetime Data Analysis. ISSN 1380-7870. 18(3), p. 261–283. doi: 10.1007/s10985-012-9214-8. Full text in Research Archive
• Ahmad, Aahshi Ambareen Sarfraz & Samuelsen, Sven Ove (2012). Hypertensive disorders in pregnancy and fetal death at different gestational lengths: a population study of 2 121 371 pregnancies. BJOG: An International Journal of Obstetrics and Gynaecology. ISSN 1470-0328. 119(12), p. 1521–1528. doi: 10.1111/j.1471-0528.2012.03460.x. Full text in Research Archive
• Gjerde, Hallvard; Normann, Per Trygve; Christophersen, Asbjørg S.; Samuelsen, Sven Ove & Mørland, Jørg (2011). Alcohol, psychoactive drugs and fatal road traffic accidents in Norway: A case-control study. Accident Analysis and Prevention. ISSN 0001-4575. 43(3), p. 1197–1203. doi: 10.1016/j.aap.2010.12.034. Full text in Research Archive
• Haavaldsen, Marit Camilla; Samuelsen, Sven Ove & Eskild, Anne (2011). The association of maternal age with placental weight: a population-based study of 536 954 pregnancies. BJOG: An International Journal of Obstetrics and Gynaecology. ISSN 1470-0328. 118(12), p. 1470–1476. doi: 10.1111/j.1471-0528.2011.03053.x. Full text in Research Archive
• Sarfraz, Aahshi Ambareen; Samuelsen, Sven Ove & Eskild, Anne (2011). Changes in fetal death during 40 years-different trends for different gestational ages: a population-based study in Norway. BJOG: An International Journal of Obstetrics and Gynaecology. ISSN 1470-0328. 118(4), p. 488–494. doi: 10.1111/j.1471-0528.2010.02819.x. Full text in Research Archive
• Vikanes, Åse Vigdis; Grjibovski, Andrej; Vangen, Siri; Gunnes, Nina; Samuelsen, Sven Ove & Magnus, Per (2010). Maternal body composition, smoking, and hyperemesis gravidarum. Annals of Epidemiology. ISSN 1047-2797. 20(8), p. 592–598. doi: 10.1016/j.annepidem.2010.05.009. Full text in Research Archive
• Stigum, Hein; Samuelsen, Sven Ove & Træen, Bente (2010). Analysis of first coitus. Archives of Sexual Behavior. ISSN 0004-0002. 39(4), p. 907–914. doi: 10.1007/s10508-009-9494-6. Full text in Research Archive
• Aamodt, Geir; Søgaard, Anne-Johanne; Næss, Øyvind Erik; Beckstrøm, Anne Cathrine & Samuelsen, Sven Ove (2010). CONOR-databasen - et lite stykke Norge. Tidsskrift for Den norske legeforening (Tidsskriftet). ISSN 0029-2001. 130(3), p. 264–265. Full text in Research Archive
• Haavaldsen, Marit Camilla; Sarfraz, Aahshi Ambareen; Samuelsen, Sven Ove & Eskild, Anne (2010). The impact of maternal age on fetal death: does length of gestation matter? American Journal of Obstetrics and Gynecology. ISSN 0002-9378. 203(6), p. 554.e1–554.e8. doi: 10.1016/j.ajog.2010.07.014. Full text in Research Archive
• Rasmussen, Trond; Stene, Lars Christian; Samuelsen, Sven Ove; Cinek, Ondrej; Wetlesen, Turid Bjørnstad & Torjesen, Peter A [Show all 7 contributors for this article] (2009). Maternal BMI before pregnancy, maternal weight gain during pregnancy, and risk of persistent positivity for multiple diabetes-associated autoantibodies in children with the high-risk HLA genotype: the MIDIA study. Diabetes Care. ISSN 0149-5992. 32(10), p. 1904–1906. doi: 10.2337/dc09-0663. Full text in Research Archive
• Samuelsen, Sven Ove; Bakketeig, Leiv Sigmund; Tretli, Steinar; Johannesen, Tom B & Magnus, Per (2009). Birth weight and childhood cancer. Epidemiology. ISSN 1044-3983. 20(4), p. 484–487. doi: 10.1097/EDE.0b013e3181a7786d. Full text in Research Archive
• Brantsæter, Anne Lise; Haugen, Margaretha; Samuelsen, Sven Ove; Torjusen, Hanne; Trogstad, Lill-Iren Schou & Alexander, Jan [Show all 8 contributors for this article] (2009). A dietary pattern characterized by high intake of vegetables, fruits, and vegetable oils is associated with reduced risk of preeclampsia in nulliparous pregnant Norwegian Women. Journal of Nutrition. ISSN 0022-3166. 139(6), p. 1162–1168. doi: 10.3945/jn.109.104968. Full text in Research Archive
• Sarfraz, AA; Samuelsen, Sven Ove; Bruu, AL; Jenum, PA & Eskild, Anne (2009). Maternal human parvovirus B19 infection and the risk of fetal death and low birthweight: a case-control study within 35 940 pregnant women. BJOG: An International Journal of Obstetrics and Gynaecology. ISSN 1470-0328. 116(11), p. 1492–1497. doi: 10.1111/j.1471-0528.2009.02211.x. Full text in Research Archive
• Småstuen, Milada C; Samuelsen, Sven Ove; Magelssen, Henriette & Fosså, Sophie Dorothea (2009). Reproduction Rates After Cancer Treatment: Experience From the Norwegian Radium Hospital. Journal of Clinical Oncology. ISSN 0732-183X. 27(3), p. 334–343. doi: 10.1200/JCO.2007.15.3130. Full text in Research Archive
• Jønsson, Viggo; Tjønnfjord, Geir Erland; Johannesen, T.B.; Samuelsen, Sven Ove & Ly, Bernt Erik (2008). Possible Imprinting and Microchimerism in Chronic Lymphocytic Leukemia and Related Lymphoproliferative Disorders. Translational Oncogenomics. 3, p. 1–6. Full text in Research Archive
• Samuelsen, Sven Ove & Eide, Geir Egil (2008). Attributable fractions with survival data. Statistics in Medicine. ISSN 0277-6715. 27(9), p. 1447–1467. doi: 10.1002/sim.3022. Full text in Research Archive
• Olsen, AL; Johannesen, TB; Ly, Bernt Erik; Samuelsen, Sven Ove; Tjønnfjord, Geir Erland & Jønsson, Viggo (2008). Pleiotropy in families with chronic lymphocytic leukemia. Salud (i) Ciencia. ISSN 1667-8982. 15, p. 1236–+. Full text in Research Archive
• Brantsæter, Anne Lise; Haugen, Alice Margaretha; Rasmusen, Salka E; Alexander, Jan; Samuelsen, Sven Ove & Meltzer, Helle Margrete (2007). Urine flavonoids and plasma carotenoids in the validation of fruit, vegetable and tea intake during pregnancy in the Norwegian Mother and Child Cohort Study (MoBa). Public Health Nutrition (PHN). ISSN 1368-9800. 10(8), p. 838–847. doi: 10.1017/S1368980007339037. Full text in Research Archive
• Samuelsen, Sven Ove; Anestad, H & Skrondal, A (2007). Stratified case-cohort analysis of general cohort sampling designs. Scandinavian Journal of Statistics. ISSN 0303-6898. 34. doi: 10.1111/j.1467-9469.2006.00552.x. Full text in Research Archive
• Jønsson, Viggo; Tjønnfjord, Geir Erland; Samuelsen, Sven Ove; Johannesen, Tom; Olsen, Jørgen & Sellick, Gabrielle [Show all 9 contributors for this article] (2007). Birth order pattern in the inheritance of chronic lymphocytic leukaemia and related lymphoproliferative disease. Leukemia and Lymphoma. ISSN 1042-8194. 48(12), p. 2387–2396. doi: 10.1080/10428190701686273. Full text in Research Archive
• Eberhard-Gran, Malin M C; Eskild, Anne; Samuelsen, Sven Ove & Tambs, Kristian (2007). A short matrix-version of the Edinburgh Depression Scale. Acta Psychiatrica Scandinavica. ISSN 0001-690X. 116(3), p. 195–200. doi: 10.1111/j.1600-0447.2006.00934.x. Full text in Research Archive
• Pedersen, Willy; Eskild, Anne & Samuelsen, Sven Ove (2006). Abort hos unge kvinner - betydningen av oppvekst og sosial klasse. Tidsskrift for Den norske legeforening (Tidsskriftet). ISSN 0029-2001. 126(13-14), p. 1734–1737. Full text in Research Archive
• Samuelsen, Sven Ove; Bakketeig, Leiv Sigmund; Tretli, Steinar; Johannesen, Tom B & Magnus, Per (2006). Head circumference at birth and risk of brain cancer in childhood: a population-based study. The Lancet Oncology. ISSN 1470-2045. 7(1), p. 39–42. doi: 10.1016/S1470-2045(05)70470-8. Full text in Research Archive
• Nystad, Wenche; Samuelsen, Sven Ove; Nafstad, Per & Langhammer, A (2006). Association between level of physical activity and lung function among Norwegian men and women: the HUNT study. The International Journal of Tuberculosis and Lung Disease. ISSN 1027-3719. 10(12), p. 1399–1405. Full text in Research Archive
• Arntzen, Annett; Samuelsen, SO; Daltveit, Anne Kjersti Nesje & Stoltenberg, Camilla (2006). Post-neonatal mortality in Norway 1969-95: a cause-specific analysis. International Journal of Epidemiology. ISSN 0300-5771. 35(4), p. 1083–1089. doi: 10.1093/ije/dyl047. Full text in Research Archive
• Aamodt, Geir; Samuelsen, Sven Ove & Skrondal, Anders (2006). A simulation study of three methods for detecting disease clusters. International Journal of Health Geographics. 5(15). doi: 10.1186/1476-072X-5-15. Full text in Research Archive Show summary

  Background Cluster detection is an important part of spatial epidemiology because it can help identifying environmental factors associated with disease and thus guide investigation of the aetiology of diseases. In this article we study three methods suitable for detecting local spatial clusters: (1) a spatial scan statistic (SaTScan), (2) generalized additive models (GAM) and (3) Bayesian disease mapping (BYM). We conducted a simulation study to compare the methods. Seven geographic clusters with different shapes were initially chosen as high-risk areas. Different scenarios for the magnitude of the relative risk of these areas as compared to the normal risk areas were considered. For each scenario the performance of the methods were assessed in terms of the sensitivity, specificity, and percentage correctly classified for each cluster. Results The performance depends on the relative risk, but all methods are in general suitable for identifying clusters with a relative risk larger than 1.5. However, it is difficult to detect clusters with lower relative risks. The GAM approach had the highest sensitivity, but relatively low specificity leading to an overestimation of the cluster area. Both the BYM and the SaTScan methods work well. Clusters with irregular shapes are more difficult to detect than more circular clusters. Conclusion Based on our simulations we conclude that the methods differ in their ability to detect spatial clusters. Different aspects should be considered for appropriate choice of method such as size and shape of the assumed spatial clusters and the relative importance of sensitivity and specificity. In general, the BYM method seems preferable for local cluster detection with relatively high relative risks whereas the SaTScan method appears preferable for lower relative risks. The GAM method needs to be tuned (using cross-validation) to get satisfactory results.

• Eggesbø, Merete; Botten, Grete Synøve; Stigum, Hein; Samuelsen, Sven Ove; Brunenkreef, B & Magnus, Per (2005). Cesarean delivery and cow milk allergy/intolerance. Allergy. European Journal of Allergy and Clinical Immunology. ISSN 0105-4538. 60, p. 1172–1173. Full text in Research Archive
• Samuelsen, Sven Ove; Wisløff, Torbjørn Fosen & Skrondal, Anders (2005). A simple correction for ties when censoring times depend on covariates. Statistics in Medicine. ISSN 0277-6715. 24(20), p. 3111–3121. doi: 10.1002/sim.2173. Full text in Research Archive
• Samuelsen, Sven Ove; Wisløff, TF & Skrondal, Anders (2005). A simple correction for ties when censoring times depend on covariates. Statistics in Medicine. ISSN 0277-6715. 24(20), p. 3111–3121. Full text in Research Archive Show summary

  We point out that the conventional methods for ties correction may be seriously biased when censoring times depend on covariates. A simple modification to the Efron correction method is suggested which works remarkably well in simulation studies. The method Corresponds closely to breaking ties by random ordering. The modified correction method is easy to implement and computationally no more demanding than the Efron correction.

• Nafstad, Per; Samuelsen, Sven Ove; Samuelsen, S; Irgens, Lorentz M. & Bjerkedal, Tor (2005). Svangerskapskomplikasjoner og risikoen for astma blant nordmenn født 1967-1993. Norsk Epidemiologi. ISSN 0803-2491. 15(1), p. 47–54. Full text in Research Archive
• Nafstad, Per; Samuelsen, Sven Ove; Irgens, Lorentz M & Bjerkedal, Tor (2005). Svangerskapskomplikasjoner og risikoen for astma blant nordmenn født 1967-1993. Norsk Epidemiologi. ISSN 0803-2491. 15(1), p. 47–54. Full text in Research Archive
• Eggesbø, Merete Åse; Botten, G; Stigum, Hein; Samuelsen, Sven Ove; Breunekreef, B & Magnus, Per (2005). Cesarean delivery and cow milk allergy/intolerance. Allergy. European Journal of Allergy and Clinical Immunology. ISSN 0105-4538. 60(9), p. 1172–1173. doi: 10.1111/j.1398-9995.2005.00857.x. Full text in Research Archive
• Arntzen, Annett; Samuelsen, Sven Ove; Bakketeig, Leiv S & Stoltenberg, Camilla (2005). A. Arntzen og medarbeidere svarer:. Tidsskrift for Den norske legeforening (Tidsskriftet). ISSN 0029-2001. 125(Årg. 125, nr 3), p. 1–1. Full text in Research Archive
• Arntzen, Annett; Samuelsen, Sven Ove; Bakketeig, Leiv S & Stoltenberg, Camilla (2004). Foreldres utdanning og spedbarnsdødelighet 1967-98. Tidsskrift for Den norske legeforening (Tidsskriftet). ISSN 0029-2001. 124(Årg. 124, nr 22), p. 2904–2906. Full text in Research Archive

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• Kvalvaag, Elisabeth Myrset; Maltzahn, Niklas Nyboe; Hjellvik, Vidar; Anjum, Mariam; Skovlund, Eva & Wisløff, Torbjørn [Show all 17 contributors for this article] (2026). Factors associated with initiation of oral anticoagulants in atrial fibrillation. Full text in Research Archive
• Samuelsen, Sven Ove & Aalen, Odd O. (2023). Special issue dedicated to Ørnulf Borgan. 29(2), p. 253–255. doi: 10.1007/s10985-023-09592-w. Full text in Research Archive
• Finnes, Trine Elisabeth; Lofthus, Cathrine Marie; Søgaard, Anne-Johanne; Tell, Grethe Seppola; Apalset, Ellen M & Gjesdal, Clara Gram [Show all 12 contributors for this article] (2015). Low serum vitamin K1 increases the risk of hip fractures only at low vitamin D status. A NOREPOS study. European Geriatric Medicine. ISSN 1878-7649. 6, p. S17–S17. Full text in Research Archive
• Støer, Nathalie; Meyer, Haakon E & Samuelsen, Sven Ove (2014). Reuse of controls in nested case-control studies. Epidemiology. ISSN 1044-3983. 25(2), p. 315–317. doi: 10.1097/EDE.0000000000000057. Full text in Research Archive
• Midtervoll, Ingvild K.; Enersen, Morten; Kristoffersen, Anne Karin; Samuelsen, Sven Ove & Håheim, Lise Lund (2014). Detection of Periodontal Pathogens in Blood from Patients With Cardiovascular Disease. Oral Presentation. Full text in Research Archive
• Midtervoll, Ingvild K.; Enersen, Morten; Kristoffersen, Anne Karin; Samuelsen, Sven Ove; Olsen, Ingar & Håheim, L.L. (2014). Detection of Periodontal Pathogens in Blood from Patients with Cardiovascular Disease. Poster presentation. Full text in Research Archive
• Holvik, Kristin; Gjesdal, Clara Gram; Tell, Grethe S; Grimnes, Guri; Schei, Berit & Apalset, Ellen M [Show all 10 contributors for this article] (2013). Low serum concentrations of vitamin E are associated with increased risk of hip fracture in older Norwegians. A NOREPOS study. Norsk Epidemiologi, Supplement. ISSN 0803-4206. 23, p. 21–21. Full text in Research Archive Show summary

  Aim: We aimed to study the association between α-tocopherol concentrations in serum and risk of hip fractures in older men and women. Methods: In the Norwegian Epidemiologic Osteoporosis Studies (NOREPOS) we performed a case-cohort analysis in 21,774 men and women aged 65-79 years (mean 72 y) who underwent baseline examinations in four community-based health studies during 1994-2001. Data on incident hip fractures were retrieved from electronic patient administrative systems. Frozen serum samples from baseline were analyzed in participants who suffered a hip fracture during median 8.2 years of follow-up (n=1168) and in sex-stratified random samples from baseline (n=1434). α-tocopherol was determined by high pressure liquid chromatography (HPLC)-fluorescence detection. Cox proportional hazards regression adapted for the case-cohort design was performed with adjustment for age, sex, and study center. Results: We observed a linear inverse relation between serum α-tocopherol levels and hip fracture, with hazard ratio (HR) 1.11 (95% CI 1.04-1.20) per 10 µmol/l lower serum α-tocopherol. HR of hip fracture in the lowest (<22.6 µmol/l) compared with the highest (>=38.3 µmol/l) quartile of serum α-tocopherol was 1.51 (95% CI 1.17-1.95). Adjustment for serum concentrations of 25(OH)D and retinol, smoking, month of blood sample, body mass index, education, physical inactivity and self-rated health yielded similar results. Conclusion: Low serum concentrations of α-tocopherol were associated with increased risk of hip fracture in older Norwegian men and women.

• Håberg, Siri Eldevik; Trogstad, Lill; Gunnes, Nina; Wilcox, Allen J; Gjessing, Håkon K. & Samuelsen, Sven Ove [Show all 19 contributors for this article] (2013). Risk of Fetal Death After Pandemic Influenza Virus Infection or Vaccination EDITORIAL COMMENT. Obstetrical and Gynecological Survey. ISSN 0029-7828. 68(5), p. 348–349. doi: 10.1097/01.ogx.0000430377.29993.2b. Full text in Research Archive
• Midtervoll, Ingvild K.; Kristoffersen, Anne Karin; Enersen, Morten; Samuelsen, Sven Ove & Håheim, Lise Lund (2013). PERIODONTAL PATHOGENS – A POSSIBLE ROLE IN CARDIOVASCULAR DISEASE? Full text in Research Archive Show summary

  Objective: The aim of this ongoing study is to investigate a possible role for periodontal pathogens in relation to cardiovascular disease (CVD) through detection of bacterial DNA in bloodsamples from participants of the Oslo II study. Materials and methods: The study design is a blinded case-cohort design where the cohort is men from Oslo, born between 1926 and 1932. The test group consists of 225 individuals who have died from CVD (myocardial infarction, aortic aneurysms or stroke), and the control group are 225 healthy men randomly picked from the cohort. After DNA extraction from blood samples in both groups, PCR amplification of the 16S rRNA bacterial gene will be performed, and PCR products of 650bp fragment will be verified on a 1,5% agarose gel. Bacterial species will be detected by high throughput sequencing of the PCR products, and results from test and control group will be correlated. Furthermore, results from three diagnoses in the test group will also be correlated separately to the controls. Correction for known risk factors such as smoking, physical inactivity, high blood pressure, total serum cholesterol and diabetes will be performed. Results: Preliminary results from PCR amplification of 260 blinded bloodsamples indicate bacterial DNA detection with the expected fragment size in 124 (48%) of the samples investigated so far.

• Holvik, Kristin; Samuelsen, Sven Ove; Ahmed, Luai Awad; Forsmo, Siri; Gjesdal, Clara Gram & Grimnes, Guri [Show all 10 contributors for this article] (2012). Low serum levels of vitamins D and A predict hip fracture in the elderly. A multicenter case-cohort study within the Norwegian Epidemiologic Osteoporosis Studies (NOREPOS). Full text in Research Archive Show summary

  Background: Norwegians have among the highest hip fracture rates worldwide. Vitamin D status is generally good and vitamin A intake is relatively high in Norway. Increased fracture risk at high intakes and serum levels of retinol have been observed in earlier epidemiologic studies. Objective: To study whether serum concentration of vitamins D and A in elderly Norwegians are related to risk of hip fracture, and whether high serum vitamin A (retinol) may counteract a possible protective effect of vitamin D. Methods: N=21,774 men and women aged 65-79 attended four community-based health studies during 1994- 2001. Subsequent hip fractures were retrieved from hospitals’ patient administrative systems, with maximum follow-up 10.7 years. 25(OH)D was determined by HPLC-APCI-MS and retinol by HPLC-UV in baseline serum samples in cases and weighted random samples of men and women. Adjusted Cox proportional hazards regression modified for the case-cohort design was performed using R. Results: During median follow-up 8.2 years, 340 men (3.4%) and 892 women (7.5%) suffered a hip fracture. We found an inverse association between 25(OH)D and hip fracture; HR 1.35 (95% CI 1.07-1.70) for <50 nmol/l compared with >75 nmol/l. Compared with middle retinol levels (2-3 μmol/l), low levels (<2 μmol/l) was associated with increased hip fracture risk: HR 1.27 (95% CI 1.00-1.62). In stratified analyses, the inverse association between 25(OH)D and risk of hip fracture was apparent at low retinol levels in men, but only at high retinol levels in women. Conclusion: Both 25(OH)D and retinol were inversely associated with risk of hip fracture.

• Vikanes, Åse Vigdis; Stoer, NC; Gunnes, Nina; Grjibovski, Andrei M.; Samuelsen, Sven Ove & Magnus, Per [Show all 7 contributors for this article] (2012). Helicobacter pylori and severe hyperemesis gravidarum by IgG, virulence factors and feces antigens; an institution-based case-control study among immigrant women in Norway. European Journal of Public Health. ISSN 1101-1262. 22, p. 240–240. Full text in Research Archive
• Vikanes, Åse Vigdis; Grjibovski, Andrej; Gunnes, Nina; Magnus, Per; Haugen, Margaretha & Støer, Nathalie [Show all 12 contributors for this article] (2012). Hyperemesis gravidarum - what is new? Highlights from seven Norwegian epidemiological studies. Acta Obstetricia et Gynecologica Scandinavica. ISSN 0001-6349. 91, p. 141–141. Full text in Research Archive
• Holvik, Kristin; Ahmed, Luai A.; Blomhoff, Rune; Forsmo, Siri; Gjesdal, Clara Gram & Grimnes, Guri [Show all 10 contributors for this article] (2012). Vitamin D status in home-dwelling elderly across Norway and prospective risk of hip fracture. A case-cohort study within the Norwegian Epidemiologic Osteoporosis Studies (NOREPOS). Full text in Research Archive
• Holvik, Kristin; Ahmed, Luai A.; Blomhoff, Rune; Forsmo, Siri; Gjesdal, Clara Gram & Grimnes, Guri [Show all 10 contributors for this article] (2012). Vitamin D status and the risk of hip fracture in elderly in Norway. A four-center case-cohort study within the Norwegian Epidemiologic Osteoporosis Studies (NOREPOS). Full text in Research Archive Show summary

  Objective: The relationship between vitamin D status and risk of hip fracture has not been established. Our aim was to study this relationship in a population-based case-cohort study of elderly men and women in Norway. Methods: N=21,774 men and women aged 65-79 years attended baseline examinations in four population-based health studies in Norway during 1994-2001. Subsequent hip fractures were retrieved from patient administrative systems and verified by X-ray or medical records, with maximum follow-up 10.7 years. All hip fracture cases and randomly sampled gender-specific subcohorts of men (4.5% yielding n=444) and women (9.0% yielding n=1058) were selected for analysis of 25-hydroxyvitamin D (25(OH)D) in serum samples from baseline stored at −80°C. 25(OH)D2 and 25(OH)D3 was determined by HPLC-APCI-MS. We performed Cox proportional hazards regression of hip fracture vs. quartiles of total 25(OH)D, with left-truncation for age at baseline and right-censoring for age at exit, inverse probability weighting and robust variance, adjusted for study site. Additional analyses were adjusted for season of blood sample, body mass index, daily cigarette smoking, and self-rated health. Results: During a median follow-up of 8.2 years, 1232 individuals (340 men (3.4%) and 892 women (7.5%)) sustained a hip fracture. The subcohorts included 1502 individuals of whom 93 were also cases. Intact frozen serum was available and successfully analysed in n=2526 (95.6%). In men, there was a trend of increasing risk of hip fracture with decreasing 25(OH)D, statistically significant for Q1 (<43.3 nmol/l) vs. Q4 (>=69.2 nmol/l): HR 1.68 (95% CI 1.05-2.68) in the main analysis, and HR 1.65 (95% CI 1.01-2.67) in the fully adjusted analysis. In women, there was no significant relation between 25(OH)D and hip fracture. However, there was a tendency of increased HR in decreasing quartiles of 25(OH)D in adjusted analysis, with HR 1.19 (95% CI 0.90-1.59) in Q1 (<41.5 nmol/l) vs. Q4 (>=67.0 nmol/l). Conclusion: According to these preliminary analyses, lower vitamin D status was significantly associated with increased HR of hip fracture in men, but not women.

• Håberg, Siri Eldevik; Trogstad, Lill; Gunnes, Nina; Gjessing, Håkon K.; Samuelsen, Sven Ove & Cappelen, Inger [Show all 17 contributors for this article] (2012). The 2009 Influenza Pandemic, Vaccination during Pregnancy and Fetal Death: A National Registry-Based Study in Norway. Pharmacoepidemiology and Drug Safety. ISSN 1053-8569. 21, p. 382–382. Full text in Research Archive
• Arntzen, Annett; Samuelsen, Sven Ove; Vangen, Siri & Stoltenberg, Camilla (2012). Have immigrants in Norway higher risk of stillbirth and infant mortality? European Journal of Public Health. ISSN 1101-1262. 22(supp. 2), p. 10–11. Full text in Research Archive
• Haavaldsen, Camilla; Sarfraz, Aahshi Ambareen; Samuelsen, Sven Ove & Eskild, Anne (2011). The Impact of Maternal Age on Fetal Death: Does Length of Gestation Matter? Obstetrical and Gynecological Survey. ISSN 0029-7828. 66(4), p. 185–186. doi: 10.1097/OGX.0b013e3182114936. Full text in Research Archive
• Cvancarova, Milada; Samuelsen, Sven Ove & Fosså, Sophie Dorothea (2009). Reproduction Rates After Cytotoxic Therapy Reply. Journal of Clinical Oncology. ISSN 0732-183X. 27(27), p. E120–E120. doi: 10.1200/JCO.2009.23.5895. Full text in Research Archive
• Jønsson, Viggo; Samuelsen, Sven Ove; Tjønnfjord, Geir Erland & johannesen, tom (2008). Looking for CLL genes. Leukemia and Lymphoma. ISSN 1042-8194. 49, p. 10–11. doi: 10.1080/10428190701713705. Full text in Research Archive
• Johannesen, Tom Børge; Ly, Bernt Erik; Samuelsen, Sven Ove; Tjønnfjord, Geir Erland & Jønsson, Viggo (2008). Ny studie om kronisk lymfatisk leukemi i Norge. Tidsskrift for Den norske legeforening (Tidsskriftet). ISSN 0029-2001. 128(6), p. 713–713. Full text in Research Archive
• Jønsson, Viggo; Tjønnfjord, Geir Erland; Samuelsen, Sven Ove; Johannesen, Tom & Ly, Bernt (2007). Pleiotrophy in familial CLL. Leukemia and Lymphoma. ISSN 1042-8194. 48, p. 124–124. Full text in Research Archive
• Eberhard-Gran, Malin; Eskild, Anne; Samuelsen, SO & Tambs, K (2007). A short matrix-version of the Edinburgh Postnatal Depression Scale. Full text in Research Archive
• Nordby, Katrine & Samuelsen, Sven Ove (2020). Dødelighet ved hoftebrudd: Analyser av kohort og matchet kohort data. Universitetet i Oslo. Full text in Research Archive Show summary

  Hoftebrudd innebærer brudd i lårhalsen eller i området ved den lille og store lårbensknuten. Vi vet at 70% av individer med hoftebrudd er kvinner og også at 70% av disse individene er over 70 år. I denne oppgaven er vi interessert i dødeligheten ved hoftebrudd. Vi skal utføre en kohortstudie der vi analyserer et datasett bestående av individer som var 50 år eller eldre i folke- og boligtellingen i Norge i 2001. Vi vil gjøre diverse undersøkelser for å beskrive dødeligheten for ulike kovariater. I hovedsak er vi interessert i å undersøke hvordan diverse kovariater påvirker dødeligheten ved hoftebrudd. Store kohortanalyser kan være både tidkrevende og kostbare. Matchede kohortanalyser der vi ser på en submengde av kohorten er et alternativ for å få ned kostnadene og tiden det tar å utføre analysene. Vi skal i denne oppgaven også utføre matchede kohortanalyser der vi matcher eksponerte individer med ikke-eksponerte individer ved hjelp av gitte matchingsvariable. Vi er interessert i hvor stor submengde, eller mer presist hvor mange ikke-eksponerte indivder vi trenger å matche hvert eksponert individ med for å oppnå omtrent like god presisjon i resultatene som ved den fulle kohorten.

• Johansen, Lena Rogstad & Samuelsen, Sven Ove (2018). Metoder og metodiske utfordringer for matchede kohortstudier. Universitetet i Oslo. Full text in Research Archive Show summary

  Når man estimerer effekten av en bestemt behandling eller eksponering på utfall i kohortstudier, og observasjonsstudier generelt, gir ikke standard metoder korrekte resultater i nærvær av ukontrollert konfundering. Matching er en teknikk som korrigerer for dette. I denne oppgaven studerer vi først og fremst i hvilken grad det er mulig å analysere matchede (også kalt tilordnede) kohortstudier når man ignorerer matchingsvariablene (konfunderingsvariablene) under forskjellige modellforutsetninger. Vi ser også på hvor mange ikke-eksponerte individer man bør velge per eksponert individ. Det viser seg at den estimerte sammenhengen mellom eksponering og utfall i nærvær versus fravær av matchingsvariablene avhenger av modellen for levetidene. Ettersom denne er både ukjent og ukontrollerbar i virkeligheten bør man beholde matchingsvariablene i analysen, såfremt det er mulig. Dessuten synes det å være lite å vinne på å velge flere enn ti ikke-eksponerte individer per eksponert individ.

• Samuelsen, Sven Ove; Ånestad, Hallvard & Skrondal, Anders (2005). Stratified case-cohort analysis of general cohort sampling designs. Universitetet i Oslo. Full text in Research Archive Show summary

  We first point out that variance estimates for regression coefficients in exposure stratified case-cohort studies (Borgan et al., 2000) can easily be obtained from influence terms routinely calculated in standard software for Cox regression. We also place the estimators proposed by Chen (2001) for a general class of cohort sampling designs within the Borgan et al. framework by allowing for post-stratification on outcome. This facilitates simple variance estimation for this class of cohort sampling designs. Finally, we extend the approach of Chen to accommodate stratified designs with surrogate variables available for all cohort members, such as stratified case-cohort and counter-matching designs.

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