Stockholms universitet

Sven DrefahlUniversitetslektor, Docent

Om mig

I am a Senior Lecturer in Demography. My research spans a range of interdisciplinary topics at the intersection of Demography, Sociology, Epidemiology, Public Health, and Statistics. Currently, I am studying the relationship between migration and mortality, determinants of COVID-19 mortality, and the ageing of the Swedish population. The majority of my work is based on individual-level register data of the total Swedish population. Beyond that I am also interested in international trends of health and mortality and demographic methods.

I am currently teaching demographic methods and statistical methods at the advanced level. Given that I am a Demographer using mainly longitudinal register data I have expert knowledge on most flavours of hazard regression (aka survival analysis, aka event-history analysis). I have also a longstanding interest in demographic microsimulations.

For my CV and more details please check also my personal website(Click here)



I urval från Stockholms universitets publikationsdatabas

  • Trends in Hip Fracture Incidence, Recurrence, and Survival by Education and Comorbidity: A Swedish Register-based Study

    2021. Anna C. Meyer (et al.). Epidemiology 32 (3), 425-433


    Background: Hip fractures are common and severe conditions among older individuals, associated with high mortality, and the Nordic countries have the highest incidence rates globally. With this study, we aim to present a comprehensive picture of trends in hip fracture incidence and survival in the older Swedish population stratified by education, birth country, and comorbidity level.

    Methods: This study is based on a linkage of several population registers and included the entire population over the age of 60 living in Sweden. We calculated age-standardized incidence rates for first and recurrent hip fractures as well as age-standardized proportions of patients surviving 30 and 365 days through the time period 1998 to 2017. We calculated all outcomes for men and women in the total population and in each population stratum.

    Results: Altogether, we observed 289,603 first hip fractures during the study period. Age-standardized incidence rates of first and recurrent fractures declined among men and women in the total population and in each educational-, birth country-, and comorbidity group. Declines in incidence were more pronounced for recurrent than for first fractures. Approximately 20% of women and 30% of men died within 1 year of their first hip fracture. Overall, survival proportions remained constant throughout the study period but improved when taking into account comorbidity level.

    Conclusions: Hip fracture incidence has declined across the Swedish population, but mortality after hip fracture remained high, especially among men. Hip fracture patients constitute a vulnerable population group with increasing comorbidity burden and high mortality risk.

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  • Intermarriage and COVID-19 mortality among immigrants. A population-based cohort study from Sweden

    2021. Siddartha Aradhya (et al.). BMJ Open 11 (9)


    Objectives To evaluate the role of language proficiency and institutional awareness in explaining excess COVID-19 mortality among immigrants.Design Cohort study with follow-up between 12 March 2020 and 23 February 2021.

    Setting Swedish register-based study on all residents in Sweden.

    Participants 3 963 356 Swedish residents in co-residential unions who were 30 years of age or older and alive on 12 March 2020 and living in Sweden in December 2019.

    Outcome measures Cox regression models were conducted to assess the association between different constellations of immigrant-native couples (proxy for language proficiency and institutional awareness) and COVID-19 mortality and all other causes of deaths (2019 and 2020). Models were adjusted for relevant confounders.

    Results Compared with Swedish-Swedish couples (1.18 deaths per thousand person-years), both immigrants partnered with another immigrant and a native showed excess mortality for COVID-19 (HR 1.43; 95%CI 1.29 to 1.58 and HR 1.24; 95%CI 1.10 to 1.40, respectively), which translates to 1.37 and 1.28 deaths per thousand person-years. Moreover, similar results are found for natives partnered with an immigrant (HR 1.15; 95%CI 1.02 to 1.29), which translates to 1.29 deaths per thousand person-years. Further analysis shows that immigrants from both high-income and low-income and middleincome countries (LMIC) experience excess mortality also when partnered with a Swede. However, having a Swedish-born partner is only partially protective against COVID-19 mortality among immigrants from LMIC origins.

    Conclusions Language barriers and/or poor institutional awareness are not major drivers for the excess mortality from COVID-19 among immigrants. Rather, our study provides suggestive evidence that excess mortality among immigrants is explained by differential exposure to the virus.

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  • A population-based cohort study of socio-demographic risk factors for COVID-19 deaths in Sweden

    2020. Sven Drefahl (et al.). Nature Communications 11 (1)


    As global deaths from COVID-19 continue to rise, the world's governments, institutions, and agencies are still working toward an understanding of who is most at risk of death. In this study, data on all recorded COVID-19 deaths in Sweden up to May 7, 2020 are linked to high-quality and accurate individual-level background data from administrative registers of the total population. By means of individual-level survival analysis we demonstrate that being male, having less individual income, lower education, not being married all independently predict a higher risk of death from COVID-19 and from all other causes of death. Being an immigrant from a low- or middle-income country predicts higher risk of death from COVID-19 but not for all other causes of death. The main message of this work is that the interaction of the virus causing COVID-19 and its social environment exerts an unequal burden on the most disadvantaged members of society. Better understanding of who is at highest risk of death from COVID-19 is important for public health planning. Here, the authors demonstrate an unequal mortality burden associated with socially disadvantaged groups in Sweden.

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  • Residential context and COVID-19 mortality among adults aged 70 years and older in Stockholm: a population-based, observational study using individual-level data

    2020. Maria Brandén (et al.). The Lancet Healthy Longevity 1 (2), e80-e88


    Background Housing characteristics and neighbourhood context are considered risk factors for COVID-19 mortality among older adults. The aim of this study was to investigate how individual-level housing and neighbourhood characteristics are associated with COVID-19 mortality in older adults.

    Methods For this population-based, observational study, we used data from the cause-of-death register held by the Swedish National Board of Health and Welfare to identify recorded COVID-19 mortality and mortality from other causes among individuals (aged ≥70 years) in Stockholm county, Sweden, between March 12 and May 8, 2020. This information was linked to population-register data from December, 2019, including socioeconomic, demographic, and residential characteristics. We ran Cox proportional hazards regressions for the risk of dying from COVID-19 and from all other causes. The independent variables were area (m2) per individual in the household, the age structure of the household, type of housing, confirmed cases of COVID-19 in the borough, and neighbourhood population density. All models were adjusted for individual age, sex, country of birth, income, and education.

    Findings Of 279 961 individuals identified to be aged 70 years or older on March 12, 2020, and residing in Stockholm in December, 2019, 274 712 met the eligibility criteria and were included in the study population. Between March 12 and May 8, 2020, 3386 deaths occurred, of which 1301 were reported as COVID-19 deaths. In fully adjusted models, household and neighbourhood characteristics were independently associated with COVID-19 mortality among older adults. Compared with living in a household with individuals aged 66 years or older, living with someone of working age (<66 years) was associated with increased COVID-19 mortality (hazard ratio 1·6; 95% CI 1·3–2·0). Living in a care home was associated with an increased risk of COVID-19 mortality (4·1; 3·5–4·9) compared with living in independent housing. Living in neighbourhoods with the highest population density (≥5000 individuals per km2) was associated with higher COVID-19 mortality (1·7; 1·1–2·4) compared with living in the least densely populated neighbourhoods (0 to <150 individuals per km2).

    Interpretation Close exposure to working-age household members and neighbours is associated with increased COVID-19 mortality among older adults. Similarly, living in a care home is associated with increased mortality, potentially through exposure to visitors and care workers, but also due to poor underlying health among care-home residents. These factors should be considered when developing strategies to protect this group.

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  • Suicide among persons who entered same-sex and opposite-sex marriage in Denmark and Sweden, 1989-2016

    2020. Annette Erlangsen (et al.). Journal of Epidemiology and Community Health 74 (1), 78-83


    Background People belonging to sexual minority groups have higher levels of suicidality than heterosexuals. However, findings regarding suicide death are sparse. Using unique national data from two countries, we investigated whether individuals entering a same-sex marriage (SSM), a proxy group of sexual minority individuals, had higher suicide rates than those entering opposite-sex marriage (OSM).

    Methods A cohort study of all males and females who entered an SSM (n=28649) or OSM (n=3 918 617) in Denmark and Sweden during 1989-2016 was conducted. Incidence rate ratios (IRRs) for suicide were calculated using adjusted Poisson regression models.

    Results In total, 97 suicides occurred among individuals who had entered an SSM compared with 6074 among those who entered an OSM, corresponding to an adjusted IRR of 2.3 (95% CI 1.9 to 2.8). For people who entered SSM, a 46% decline was noted over time from an IRR of 2.8 (95% CI 1.9 to 4.0) during 1989-2002 to 1.5 (95% CI 1.2 to 1.9) during 2003-2016. The excess suicide mortality was present in all age groups but most pronounced among younger individuals aged 18-34 years of age (IRR 2.7, 95%CI 1.5 to 4.8) and females (IRR 2.7, 95%CI 1.8 to 3.9).

    Conclusion This large register-based study found higher suicide rates among individuals who entered an SSM, compared with those who entered an OSM. A lower suicide rate was noted for individuals in SSMs in recent years. More research is needed to identify the unique suicide risk and protective factors for sexual minority people.

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  • Trends in life expectancy

    2020. Anna C. Meyer (et al.). BMC Medicine 18 (1)


    Background During the past decades, life expectancy has continued to increase in most high-income countries. Previous research suggests that improvements in life expectancy have primarily been driven by advances at the upper end of the health distribution, while parts of the population have lagged behind. Using data from the entire Swedish population, this study aims to examine the life expectancy development among subgroups of individuals with a history of common diseases relative to that of the general population. Methods The remaining life expectancy at age 65 was estimated for each year in 1998-2017 among individuals with a history of disease, and for the total Swedish population. We defined population subgroups as individuals with a history of myocardial infarction, ischemic or hemorrhagic stroke, hip fracture, or colon, breast, or lung cancer. We further distinguished between different educational levels and Charlson comorbidity index scores. Results Life expectancy gains have been larger for men and women with a history of myocardial infarction, ischemic or hemorrhagic stroke, and colon or breast cancer than for the general population. The life expectancy gap between individuals with a history of hip fracture or lung cancer and the general population has, however, been growing. Education and comorbidity have affected mortality levels, but have not altered the rate of increase in life expectancy among individuals with disease history. The female advantage in life expectancy was less pronounced among individuals with disease history than among the general population. Conclusions Life expectancy has increased faster in many subpopulations with a history of disease than in the general population, while still remaining at lower levels. Improvements in life expectancy have been observed regardless of comorbidity or educational level. These findings suggest that the rise in overall life expectancy reflects more than just improved survival among the healthy or the delayed onset of disease.

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  • Regional trajectories in life expectancy and lifespan variation

    2020. Ben Wilson (et al.). Population, Space and Place 26 (8)


    An important dimension of inequality in mortality is regional variation. However, studies that investigate regional mortality patterns within and between national and regional borders are rare. We carry out a comparative study of Finland and Sweden: two welfare states that share many attributes, with one exception being their mortality trajectories. Although Finland has risen rapidly in the global life expectancy rankings, Sweden has lost its historical place among the top 10. Using individual-level register data, we study regional trends in life expectancy and lifespan variation by sex. Although all regions, in both countries, have experienced substantial improvements in life expectancy and lifespan inequality from 1990-2014, considerable differences between regions have remained unchanged, suggesting the existence of persistent inequality. In particular, Swedish-speaking regions in Finland have maintained their mortality advantage over Finnish-speaking regions. Nevertheless, there is some evidence of convergence between the regions of Finland and Sweden.

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  • Over-coverage in population registers leads to bias in demographic estimates

    2019. Andrea Monti (et al.). Population Studies


    Estimating the number of individuals living in a country is an essential task for demographers. This study assesses the potential bias in estimating the size of different migrant populations due to over-coverage in population registers. Over-coverage-individuals registered but not living in a country-is an increasingly pressing phenomenon; however, there is no common understanding of how to deal with over-coverage in demographic research. This study examines different approaches to and improvements in over-coverage estimation using Swedish total population register data. We assess over-coverage levels across migrant groups, test how estimates of age-specific death and fertility rates are affected when adjusting for over-coverage, and examine whether over-coverage can explain part of the healthy migrant paradox. Our results confirm the existence of over-coverage and we find substantial changes in mortality and fertility rates, when adjusted, for people of migrating age. Accounting for over-coverage is particularly important for correctly estimating migrant fertility.

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  • All-cause mortality, age at arrival, and duration of residence among adult migrants in Sweden

    2018. Sol Juárez (et al.). SSM - Population Health 6, 16-25


    Background: A mortality advantage has been observed among recently arrived immigrants in multiple national contexts, even though many immigrants experience more social disadvantage compared to natives. This is the first study to investigate the combined influence of duration of residence and age at arrival on the association between region of origin and all-cause mortality among the adult immigrant population in Sweden.

    Methods: Using population-based registers, we conducted a follow-up study of 1,363,429 individuals aged 25-64 years from 1990 to 2008. Gompertz parametric survival models were fitted to derive hazard ratios (HR) for all-cause mortality.

    Results: Compared to native Swedes, we observed a health advantage in all group of immigrants, with the exception of individuals from Finland. However, when information on age at arrival and duration of residence was combined, an excess mortality risk was found among immigrants who arrived before age 18, which largely disappeared after 15 years of residence in Sweden. Non-European immigrants over age 18 showed similar or lower mortality risks than natives in all categories of age at arrival, regardless of duration of residence.

    Conclusions: The findings suggest that the mortality advantage commonly observed among immigrants is not universal. Combined information on age at arrival and duration of residence can be used to identify sensitive periods and to identify possible selection bias. The study also suggests that young immigrants are a vulnerable subpopulation. Given the increased number of unaccompanied minors arriving in Europe, targeted health or integration policies should be developed or reviewed.

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  • Long-Distance Migration and Mortality in Sweden

    2017. Gunnar Andersson, Sven Drefahl. Population, Space and Place 23 (4)


    International migrants often have lower mortality rates than the native populations in their new host countries. Several explanations have been proposed, but in the absence of data covering the entire life courses of migrants both before and after each migration event, it is difficult to assess the validity of different explanations. In the present study, we apply hazard regressions to Swedish register data to study the mortality of long-distance migrants from Northern to Southern Sweden as well as the mortality of return migrants to the North. In this way, we can study a situation that at least partly resembles that of international migration while still having access to data covering the full demographic biographies of all migrants. This allows us to test the relative roles of salmon bias and healthy migrant status in observed mortality rates of long-distance migrants. We find no mortality differentials between residents in northern and southern Sweden, and no evidence of a selection of healthy migrants from the North to the South. In contrast, we provide clear evidence of salmon effects' in terms of elevated mortality of the return migrants to northern Sweden, which are produced when migrants return to their place of origin in relation to subsequent death.

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  • Losing Ground - Swedish Life Expectancy in a Comparative Perspective

    2014. Sven Drefahl, Anders Ahlbom, Karin Modig. PLoS ONE 9 (2), e88357


    Background: In the beginning of the 1970s, Sweden was the country where both women and men enjoyed the world's longest life expectancy. While life expectancy continues to be high and increasing, Sweden has been losing ground in relation to other leading countries. Methods: We look at life expectancy over the years 1970-2008 for men and women. To assess the relative contributions of age, causes of death, and smoking we decompose differences in life expectancy between Sweden and two leading countries, Japan and France. This study is the first to use this decomposition method to observe how smoking related deaths contribute to life expectancy differences between countries. Results: Sweden has maintained very low mortality at young and working ages for both men and women compared to France and Japan. However, mortality at ages above 65 has become considerably higher in Sweden than in the other leading countries because the decrease has been faster in those countries. Different trends for circulatory diseases were the largest contributor to this development in both sexes but for women also cancer played a role. Mortality from neoplasms has been considerably low for Swedish men. Smoking attributable mortality plays a modest role for women, whereas it is substantially lower in Swedish men than in French and Japanese men. Conclusions: Sweden is losing ground in relation to other leading countries with respect to life expectancy because mortality at high ages improves more slowly than in the leading countries, especially due to trends in cardiovascular disease mortality. Trends in smoking rates may provide a partial explanation for the trends in women; however, it is not possible to isolate one single explanatory factor for why Sweden is losing ground.

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  • The Married Really Live Longer? The Role of Cohabitation and Socioeconomic Status

    2012. Sven Drefahl. Journal of Marriage and Family 74 (3), 462-475


    Numerous studies have shown that married women and men experience the lowest mortality. Legal marital status, however, does not necessarily reflect today's social reality because individuals are classified as never married, widowed, or divorced even when they are living with a partner. Denmark is one of the forerunners of developments in coresidential partnerships and one of only a few countries where administrative sources provide individual-level information on cohabitation for the whole population. Using register information from Statistics Denmark on 3,888,072 men and women ages 18–65, the author investigated mortality differences by living arrangement with hazard regression models. Overall, premature mortality was found to be lowest for married persons, followed by cohabiting persons. Adjusting for socioeconomic status reduced excess mortality of nonmarried individuals. Moreover, a mortality-crossover effect emerged in which cohabiters with above-average socioeconomic status had a lower risk of dying than married people. This finding was particularly pronounced for men.

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  • How Does the Age Gap Between Partners Affect Their Survival?

    2010. Sven Drefahl. Demography 47 (2), 313-326


    I use hazard regression methods to examine how the age difference between spouses affects their survival. In many countries, the age difference between spouses at marriage has remained relatively stable for several decades. In Denmark, men are, on average, about three years older than the women they marry. Previous studies of the age gap between spouses with respect to mortality found that having a younger spouse is beneficial, while having an older spouse is detrimental for one's own survival. Most of the observed effects could not be explained satisfactorily until now, mainly because of methodological drawbacks and insufficiency of the data. The most common explanations refer to selection effects, caregiving in later life, and some positive psychological and sociological effects of having a younger spouse. The present study extends earlier work by using longitudinal Danish register data that include the entire history of key demographic events of the whole population from 1990 onward. Controlling for confounding factors such as education and wealth, results suggest that having a younger spouse is beneficial for men but detrimental for women, while having an older spouse is detrimental for both sexes.

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  • An application of diagonal reference models and time-varying covariates in social mobility research on mortality and fertility

    2018. Sunnee Billingsley, Sven Drefahl, Gebrenegus Ghilagaber. Social Science Research 75, 73-82


    In social mobility research, the diagonal reference model (DRM) is argued to best isolate the effect of social mobility from origin and destination status effects. In demographic research, standard analyses of the duration until an event occurs rely heavily on the appropriate use of covariates that change over time. We apply these best-practice methods to the study of social mobility and demographic outcomes in Sweden using register data that covers the years 1996–2012. The mortality analysis includes 1,024,142 women and 747,532 men and the fertility analysis includes 191,142 women and 164,368 men. We identify the challenges inherent in this combination and present strategies with an application to how social mobility is related to both fertility and mortality. Our application is successful at incorporating all requirements related to these methods. Our findings suggest, however, that certain data characteristics, such as a relatively high share of missing data, can be problematic. We also find that controlling for origin and destination status generally provides acceptable estimates of the mobility association in the specific case of Sweden and the relationship between social mobility and both fertility and mortality.

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