Demographic changes are reshaping our kinship networks. Falling fertility not only affects the number of children people have, but also the number of siblings, cousins, and grandchildren available to future generations. Furthermore, population aging influences the number of years we share with parents and grandparents, as well as the caring responsibilities that come with them. Lastly, divorce, re-partnering, and subsequent multi-partner fertility introduce new types of kin into our networks, such as half-siblings and step-grandparents.

To gain a better understanding of these changes, it is essential to map kinship networks empirically (see e.g. Jiang 2025). However, data that allow us to do so are scarce. Kolk et al (2023) recently published a study in which they counted how many relatives Swedes have. We replicated their approach work using kinship network data from the Dutch population registers (Bel et al. 2025). In our study, we focus on three birth cohorts to anchor the comparison with Sweden: 1935 to represent the pre-WW2 cohort; 1955 to represent the baby-boom generation born in the years following WW2; and 1985 to represent the generation born after the onset of the Second Demographic Transition (SDT).

Figure 1 shows the number of kin Dutch people have by age. At first glance, this picture is quite similar to the one in Sweden. However, two remarkable differences can be observed: one related to the Dutch baby boom, the other to higher multi-partner fertility in Sweden.

Dutch baby boom

Table 1 shows the number of children, nieces and nephews, siblings, cousins, and aunts and uncles that people have. It presents these counts for individuals born in 1935, 1955, and 1985. The numbers for Sweden are taken from the Swedish study (Kolk et al., 2023), while the figures for the Netherlands are newly calculated. 

Dutch women born in 1935, representing the pre-WW2 cohort, had 2.3 children on average, and 16% had four or more children, compared to 9% in Sweden (not shown in Table 1). Swedish women in the same cohort had 2.0 children on average, or 15% fewer. 

People born in 1955, the baby-boom generation, have 2.7 living siblings and 5.5 living nieces and nephews on average, i.e. 42% more siblings and 34% more nieces and nephews than their Swedish counterparts. Looking at the next generation, born in 1985, allows us to observe what we interpret as a trickle-down effect of the Dutch baby boom: people born in 1985 have 38% more aunts and uncles (5.1) and cousins (11.2) than their Swedish peers.

Multi-partner fertility in Sweden

We also observe a reversal in the average number of siblings between the two countries. Dutch people from the 1955 cohort have 2.7 siblings on average, compared to 1.9 in Sweden, which amounts to a difference of 42%. However, Dutch people born 30 years later, in 1985, have an average of 1.8 siblings, compared to 2.2 in Sweden, which is 18% fewer.

As a result of higher divorce rates in Sweden than in the Netherlands (2.8 vs. 2.0 per 100 persons in 2013; Eurostat, 2024), multi-partner fertility and the presence of half-siblings became increasingly common from the mid-20th century onward (Turunen and Kolk 2017). Consequently, the 1985 Dutch cohort has just 0.1 paternal half-sibling and on average fewer than 0.1 maternal half-siblings, compared to 0.4 paternal and 0.3 maternal half-siblings in Sweden (not shown in Table 1).

Conclusion

Our study shows similarities between Dutch and Swedish kinship networks, but it also highlights two interesting differences. First, our results suggest that the Dutch baby boom has trickled down from one generation to the next, leading to larger numbers of aunts, uncles, and cousins for people born 30 years after the boom. Second, Dutch kinship networks show a lower number of half-siblings compared to Sweden, which can be explained by lower divorce rates in The Netherlands.

References

de Bel, V., Bokányi, E., Hank, K., & Leopold, T. (2025). A parallel kinship universe? A replication of Kolk et al. (2023) with Dutch register data on kinship networks. Demographic Research, 52, 915–938. https://doi.org/10.4054/DemRes.2025.52.28

Eurostat. (2024). Divorce indicators. https://doi.org/https://doi.org/10.2908/DEMO_NDIVIND

Jiang, S. (2025) The kinship gap. When just a few years of difference make a difference, N-IUSSP, 17 November. https://www.niussp.org/fertility-and-reproduction/the-kinship-gap-when-just-a-few-years-of-difference-make-a-difference/

Kolk, M., Andersson, L., Pettersson, E., & Drefahl, S. (2023). The Swedish Kinship Universe: A Demographic Account of the Number of Children, Parents, Siblings, Grandchildren, Grandparents, Aunts/Uncles, Nieces/Nephews, and Cousins Using National Population Registers. Demography, 60(5), 1359–1385. https://doi.org/10.1215/00703370-10955240

Turunen, J., & Kolk, M. (2017). The prevalence of half-siblings over the demographic transition in Northern Sweden 1750–2007. IUSSP International Population Conference.

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Why do some people live longer than others? This question has long motivated research in public health, demography, and sociology. One consistent finding is that married individuals tend to outlive those who remain single, divorced, or widowed (Rendall et al. 2011). However, as family structures evolve – with non-marital cohabitation becoming increasingly common worldwide, and most notably in Sweden (Ohlsson-Wijk, Turunen, and Andersson 2020) – the question arises: does cohabitation offer the same longevity benefits as marriage, or is there something unique about marital unions?

The link between marriage and longevity is based on well-established social and economic advantages (Carr and Springer 2010). Given that long-term cohabitation is more commonly accepted and often resembles marriage in daily life, it is essential to determine if these protective advantages also apply to non-marital relationships.

In a recent study (Lindmarker, Kolk, and Drefahl 2025), we examined Swedish register data (2012–2017) to assess the effects of cohabitation and marriage on mortality throughout life. The findings indicate that cohabitation is less protective than marriage, but its effects differ based on age and previous marital status.

Why would a partner extend life?

The link between longevity and partnership status arises from both selection processes and protective factors. Healthier individuals are more likely to partner and remain with a partner, suggesting that part of the marriage advantage is due to selection effects (Lillard and Panis 1996). Beyond selection, partnerships confer substantial protective benefits. Social support plays a crucial role: a partner not only provides companionship, but also monitors health, encourages adherence to medications, and offers emotional comfort that counteracts the negative effects of stress. This effect is especially apparent among men, whose health behaviors are most positively affected by their partners (Umberson 1987).

Economic stability is another significant advantage. By pooling resources, couples experience reduced financial stress and improved access to healthcare. In addition, partnership tends to promote healthy habits, from maintaining regular meals and routines to avoiding risky behaviors. Caregiving and companionship provided by spouses are particularly critical in later life, when support can mitigate the risks associated with social isolation.

Cohabitation and mortality: divergent risks by age and marital history

Our study shows that married individuals generally experience the lowest risk of mortality. Cohabiters have lower mortality than unpartnered individuals, including singles, divorcees, or widow(er)s. However, their death risks vary significantly by marital history and age.

• Never-married cohabiters: At ages 30–49, never-married cohabiters have mortality risks comparable to those of married individuals. This suggests that in early adulthood, cohabitation provides protective benefits similar to marriage. However, in older age groups (50+), never-married cohabiters begin to experience higher mortality risks than married individuals. This may be due to both selection effects, as healthier individuals tend to transition into marriage, and the reduced long-term benefits of cohabitation relative to marriage.

• Divorced/Widowed cohabiters: For those who cohabit after a previous marriage, the pattern is reversed. In younger age groups, divorced or widowed cohabiters face significantly higher mortality risks than their married counterparts, likely reflecting negative selection, where union dissolution at younger ages is linked to poorer health and socioeconomic challenges. However, in older age groups, excess mortality among divorced cohabiters decreases, probably because of the increasing prevalence, in this group, of those who re-partner later in life after long marriages, carrying forward financial, social, and health advantages from their previous unions. This “double advantage” from both past stable marriages and new partnerships helps reduce the risk of mortality compared to younger divorced cohabiters.

Why do these patterns emerge?

Several factors help explain the longevity differences between cohabitation and marriage. Selection effects matter: long-term cohabiters may differ from married individuals in ways that influence health and longevity. Social support is key: while cohabitation offers companionship, it may not always provide the same level of long-term caregiving as marriage, especially later in life. Economic factors also play a role, since marriage traditionally provides greater financial security and better access to healthcare. Finally, the cumulative benefits of marriage, including reinforced healthy behaviors, legal protections, and social support, appear to confer an enduring advantage in promoting longevity.

Although cohabitation offers significant health benefits, it does not fully replicate the long-term advantages of marriage, but it is still unclear whether these differences arise from selection processes, socio-economic factors, or the distinct ways in which marriage and cohabitation shape life outcomes.

References

Carr, Deborah, and Kristen W. Springer. 2010. “Advances in Families and Health Research in the 21st Century.” Journal of Marriage and the Family. https://doi.org/10.1111/j.1741-3737.2010.00728.x.

Lillard, Lee A., and Constantijn W. A. Panis. 1996. “Marital Status and Mortality: The Role of Health.” Demography. https://doi.org/https://doi-org.ezp.sub.su.se/10.2307/2061764.

Lindmarker, Jesper, Martin Kolk, and Sven Drefahl. 2025. “Cohabitation and Mortality Across the Life Course: A Longitudinal Cohort Study with Swedish Register-Based Sibling Comparisons.” European Journal of Population 41 (1): 2. https://doi.org/10.1007/s10680-024-09722-6.

Ohlsson-Wijk, Sofi, Jani Turunen, and Gunnar Andersson. 2020. “Family Forerunners? An Overview of Family Demographic Change in Sweden.” In International Handbook on the Demography of Marriage and the Family, edited by D. Nicole Farris and A. J. J. Bourque, 7:65–77. Cham: Springer International Publishing. https://doi.org/10.1007/978-3-030-35079-6_5.

Rendall, Michael S., Margaret M. Weden, Melissa M. Favreault, and Hilary Waldron. 2011. “The Protective Effect of Marriage for Survival: A Review and Update.” Demography 48 (2): 481–506. https://doi.org/10.1007/s13524-011-0032-5.

Umberson, Debra. 1987. “Family Status and Health Behaviors: Social Control as a Dimension of Social Integration.” Journal of Health and Social Behavior 28 (3): 306–19. https://doi.org/10.2307/2136848.

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Surprisingly little is known about the composition of kinship groups and family members outside the household. Although demographers have a reputation for counting things, very few studies have counted kinship networks in contemporary societies. The lack of data is unfortunate as the extended family forms an important part of an individual’s social network and can provide significant support, ranging from child rearing and elder care to financial assistance. As recent research on social stratification indicates, the extended family background is also important for life chances in contemporary societies (Hällsten & Kolk 2022; Mare 2011).

The dynamics of kinship in Sweden 

In a recent study, my coauthors and I documented kinship in Sweden using Swedish administrative registers (Kolk, Andersson, Pettersson, & Drefahl, 2023). We counted the averages and distributions of kin such as grandchildren, children, nieces, nephews, siblings, cousins, parents, parents’ siblings, and grandparents, and we examined these relationships longitudinally, because kinship varies considerably over the life course, both quantitatively and qualitatively.

Figure 1 shows the average number of different categories of kin for Swedes of different ages observed in 2017. People in their mid-30s have the most relatives, about 20, while young children have about 15, and 70-year-olds have about 10. Not surprisingly, older people have more relatives in the descending line, such as grandchildren, while the young have the more relatives in the ascending line, such as parents and grandparents. People in mid-life have a large number of relatives in the same generation, such as siblings and cousins. Swedes in their mid-30s, for instance, have 8 cousins on average, and almost 30 percent have 11 or more. In our original study (Kolk, Andersson, Pettersson, & Drefahl, 2023), we provide more detailed figures for each category of kin, and we look at how factors such as sex, lineage (e.g. maternal and paternal grandparents) and family complexity (e.g. half-siblings) affect the number and type of relatives people have.

A strongly variable phenomenon 

Figure 2 shows that the number of relatives the Swedes have varies considerably, depending on who, and how old they are. Some people have very few relatives, only 3 or 4, while others have more than 45. It is very rare to have no relatives at all: this only happens in some exceptional cases among very old people. The family networks of men and women are very similar. Over time, the proportion of relatives who are the result of separations, such as half-siblings, tends to increase.

A few characteristics of our study and some conclusions

We used Swedish register data to conduct our study, which covers all Swedish-born people living in Sweden in 2018. We used birth records and the unique Swedish national identity numbers to create family networks and count the number of relatives for each person. However, our study only focused on Swedish-born individuals because we did not have demographic data for people living outside Sweden. This means that some relatives, especially grandparents, were missing for people with foreign-born parents. 

We think that kinship in contemporary societies should be studied more fully. The last decades have seen substantive work on what kin do, for example, as the recipients or providers of elder care, as well as their role in social mobility. In contrast, we know much less about who has kin and of what type. Here, and in our scientific paper, we give a full demographic account of kinship in one high-income society, but the patterns we find are, of course, specific to the Swedish demographic context. Whether the distributions or relatives by type and age that we found are standard or idiosyncratic is something that cannot be determined until similar data are collected for other countries and other periods. 

References

Hällsten, M., & Kolk, M. (2022). The Shadow of Peasant Past: Seven Generations of Inequality Persistence in Northern Sweden. American Journal of Sociology, 128(6), 1716-1760. 

Kolk, M., Andersson, L., Pettersson, E., & Drefahl, S. (2023). The Swedish Kinship Universe – A demographic account of the number of children, parents, siblings, grandchildren, grandparents, aunts/uncles, nieces/nephews, and cousins using national population registers. Demography, available online, 10955240.

Mare, R. D. (2011). A multigenerational view of inequality. Demography, 48(1), 1-23.

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Suicide and marriage

Suicide ranks high among the causes of death worldwide, accounting for more than one in every 100 deaths globally in 2019 (WHO 2021). A famous study on the social predictors of suicide by the sociologist Emile Durkheim first documented that suicide was less common among married people in 1897 (Durkheim 1897), and more recent research has consistently found the same pattern. Studies broadly show that marriage benefits both physical and mental health through many mechanisms, including the companionship and economic resources it provides. However, they also find that the health benefits of marriage can vary across characteristics such as race/ethnicity (Martínez et al. 2016) and gender (Gove 1973). Less research has examined whether the health benefits of marriage are linked to the immigration background of a person’s spouse. The literature supports conflicting expectations.

Intermarriage and well-being 

Intermarriage is widely considered to be one of the strongest indicators of an immigrant’s integration into a host country. Living with a native-born spouse may improve immigrants’ social integration and well-being by helping them learn the language, enhancing their understanding of the host country’s culture and social systems, and facilitating access to social networks and employment. Accordingly, intermarriage has been associated with better economic outcomes among immigrants in Sweden (Dribe and Lundh 2008). Intermarriage may also benefit native-born partners by increasing their cultural capital (Rodríguez-García 2015), which provides advantages in social life.

On the other hand, studies suggest that intermarriage predicts a greater likelihood of marital conflict. Intermarried couples may have sociocultural differences in values, norms, and communication styles. They may also be exposed to discrimination. These circumstances can reduce marital quality and may take a toll on intermarried persons’ well-being. Indeed, prior research shows that intermarriages are less stable than unions between people from the same ethnic background (Kalmijn, de Graaf, and Janssen 2005). A recent study showed that both partners in marriages between native German women and immigrant men had worse mental health than the partners in marriages involving two native-born Germans (Eibich and Liu 2021). These findings collectively imply that the relationship between marriage and mental health may differ by nativity. 

Intermarriage and suicide risk 

In a recent study (Oksuzyan et al. 2023), we investigated whether suicide risk in Sweden differs between intermarried people and those married to someone from their same ethnic background. The study used national Swedish registry data from the years 1991 to 2016. We included all married individuals aged 18 and older in our analysis (N = 6,249,727). A total of 18,116 deaths due to suicide occurred over the course of the study.

We found some evidence that intermarried people in Sweden were at greater risk of suicide. More precisely, in marriages between a native-born Swedish man and an immigrant woman, both partners were at higher risk of suicide death than in marriages where both partners were native-born Swedes (Figure 1). However, we did not find a similar elevated risk among partners in marriages between Swedish women and immigrant men. In addition, the increased suicide risk of immigrant women married to male Swedes was present only among those from non-Western countries (Figure 2). The suicide risk of intermarried immigrant women from Western nations was comparable to that of immigrant women married to other immigrants from their same country.

Why might people in marriages between a Swedish man and an immigrant woman be at greater risk of suicide? One possibility is that these marriages are characterized by more asymmetric power relations than marriages involving immigrant men and Swedish women. Immigrant men were more likely to marry “down” in terms of education when they married a native-born woman compared to when they married an immigrant woman, i.e., to trade-off their higher socioeconomic status with the “prestige” of marrying a native woman (Kalmijn and van Tubergen 2006). These unions follow the conventional gender norms that are still prevalent in Sweden and other European nations, where men are considered to be the breadwinners and women are expected to be homemakers. In contrast, there may be conflicting expectations about gender roles in binational marriages between immigrant women with a higher socioeconomic status than their local Swedish partner.

It may also be that native-born Swedish men and immigrant women with disadvantages that may increase their suicide risk, such as poorer health behaviors and mental health, are more likely to intermarry. To test for the possibility that people in these marriages have a health disadvantage and a greater risk of death more broadly, we analyzed differences in all-cause mortality by intermarriage group. However, we did not find the same elevated hazard of death for all-cause mortality among immigrant women married to native men as we did for suicide mortality. 

We also found that immigrant men and women who marry an immigrant from their same origin country had a markedly lower risk of suicide relative to Swedes married to Swedes. This finding is consistent with our initial expectation that marriages involving partners from the same ethnic background share migration experiences and are healthier, on average, than native-born persons. 

Conclusion

Our study provides preliminary evidence that some individuals in intermarriages between immigrants and native-born persons are at increased risk of suicide mortality. They signal the possibility that marrying someone with a different ethnic background may potentially introduce additional stressors to marriage, such as cultural conflict, marital discord, and relationship inequality, with long-term consequences for mental health and well-being.

References 

Dribe, Martin, and Christer Lundh. 2008. “Intermarriage and Immigrant Integration in Sweden: An Exploratory Analysis.” Acta Sociologica 51 (4): 329–54. https://doi.org/10.1177/0001699308097377.

Durkheim, Émile. 1897. Suicide: A Study in Sociology. Edited by George Simpson. New York: Free Press. https://link.springer.com/content/pdf/10.1007%2Fs13524-011-0032-5.pdf.

Eibich, Peter, and Chia Liu. 2021. “For Better or for Worse Mental Health? The Role of Family Networks in Exogamous Unions.” Population, Space and Place, no. October 2020: 1–25. https://doi.org/10.1002/psp.2437.

Gove, Walter R. 1973. “Sex, Marital Status, and Mortality.” American Journal of Sociology 79 (1): 45–67. http://www.jstor.org/stable/2776709.

Kalmijn, Matthijs, Paul M. de Graaf, and Jacques P.G. Janssen. 2005. “Intermarriage and the Risk of Divorce in the Netherlands: The Effects of Differences in Religion and in Nationality, 1974-94.” Population Studies 59 (1): 71–85. https://doi.org/10.1080/0032472052000332719.

Kalmijn, Matthijs, and Frank van Tubergen. 2006. “Ethnic Intermarriage in the Netherlands: Confirmations and Refutations of Accepted Insights.” European Journal of Population / Revue Européenne de Démographie 22 (4): 371–97. https://doi.org/10.1007/s10680-006-9105-3.

Martínez, María Elena, Kristin Anderson, James D. Murphy, Susan Hurley, Alison J. Canchola, Theresa H.M. Keegan, Iona Cheng, Christina A. Clarke, Sally L. Glaser, and Scarlett L. Gomez. 2016. “Differences in Marital Status and Mortality by Race/Ethnicity and Nativity among California Cancer Patients.” Cancer 122 (10): 1570–78. https://doi.org/10.1002/cncr.29886.

Oksuzyan, Anna, Sven Drefahl, Jennifer Caputo, and Siddartha Aradhya. 2023. “Is It Better to Intermarry? Immigration Background of Married Couples and Suicide Risk Among Native-Born and Migrant Persons in Sweden.” European Journal of Population 39 (1). https://doi.org/10.1007/s10680-023-09650-x.

Rodríguez-García, Dan. 2015. “Intermarriage and Integration Revisited: International Experiences and Cross-Disciplinary Approaches.” Annals of the American Academy of Political and Social Science 662 (1): 8–36. https://doi.org/10.1177/0002716215601397.

WHO. 2021. Suicide Worldwide in 2019. World Health Organization. Geneva. https://apps.who.int/iris/rest/bitstreams/1350975/retrieve%0Ahttps://www.who.int/publications-detail-redirect/9789240026643.

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Is it poorer or richer people who have more children? This question, central to many of the founders of social science and statistics in the 19^th and 20^th centuries, remains an important topic in demography. It is common wisdom among both the public and many researchers that poorer individuals have more children, but in a new study, I provide evidence that this idea may be incorrect, at least in Sweden (Kolk, 2022).  

Lifetime earnings and fertility

To evaluate life course income, and assess its association with childbearing, I used yearly Swedish taxation registers, restricting the analysis to national data on Swedish-born men and women, who were studied separately. Analyzing my data by birth cohorts, I summed all re-evaluated incomes over working ages. This allowed me to circumvent many of the issues related to short-term interrelations between income and childbearing, such as women leaving the labor market to take care of young children.

For men, a consistently positive gradient emerged for all cohorts: the number of children increases monotonically across income (Figure 1, panel 1a). For women, the relationship is more complicated and changes over time (Figure 1, panel 1b). Among those born in the 1940s, no or very low income (i.e., being or becoming a homemaker) is associated with the highest number of children. In later cohorts, however, the reverse is true: it is women with no or little income who have the lowest fertility, although the relationship vanishes above a certain income threshold (women of all upper income classes having similar fertility).

Much of this relationship is due to low income among childless men and women, suggesting that an increasingly large group of low socioeconomic status individuals are excluded from partnerships and childrearing (Figure 2). Lifetime incomes are highest for men and women with 2-4 children, although for very high numbers of children (5 and above, representing less than 1.5% of the population), incomes are somewhat lower. 

Both figures (1 and 2) refer to disposable income, which includes government transfers to parents, such as parental leave and child allowances. This may partly affect the findings as the Swedish welfare state provides many benefits for parents, and these are usually paid to mothers. Indeed, if we include only labor income (excluding parental leaves and child allowances), we get similar results for men, but not for women: the gradient remains negative for more birth cohorts (the richer having fewer babies), and it turns positive only for those born in the 1970s.

Implications

Previous negative associations between income and fertility may have been partly due to cultural orientations and values that differed between high and low socioeconomic status groups in Sweden (and other countries), but these differences are either shrinking or being outweighed by a new economic reality: children, who are expensive but arguably desirable to large groups in society, may be becoming a luxury that not everybody can afford.

Sweden is a society where combining wage labor and childrearing is still largely possible: some of the reasoning above may be conditioned on welfare state support for childrearing and female employment, and many of my findings may not be applicable to other contexts. Nevertheless, if I were to make a forecast for the 21^st century, I would speculate that a positive relationship between income and fertility will emerge in an increasing number of contexts all over the world, in one or more of the following forms:

• an individual-level positive gradient between personal income and fertility,
• a positive link between fertility and the business cycle, and
• higher fertility in the world’s richest countries than in less wealthy parts of the globe.

Indeed, the findings of an increasing number of studies are consistent with these patterns: e.g., Hopcroft (2022) in the US, Fox et al (2019) at the regional level in Europe, and Jalovara and Fasang (2020) in Finland.

References

Kolk, M. (2022). The relationship between life-course accumulated income and childbearing of Swedish men and women born 1940–70. Population Studies, available online

Fox, J., Klüsener, S., & Myrskylä, M. (2019). Is a positive relationship between fertility and economic development emerging at the sub-national regional level? Theoretical considerations and evidence from Europe. European Journal of Population, 35, 487‒518.

Hopcroft, R. L. (2022). Husband’s income, wife’s income, and number of biological children in the US. Biodemography and Social Biology, 67(1), 71‒83.Jalovaara, M., & Fasang, A. E. (2020). Family life courses, gender, and mid-life earnings. European sociological review, 36(2), 159‒178.

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International migrant populations are some of the most mobile populations in the world, making it difficult to accurately determine their numbers in host countries and their outcomes relative to the locally-born population. This is because many host country systems are not equipped to capture the moves of migrants into and, particularly, out of their countries. If migrants leave a host country and an exit is not recorded, they continue to exist in host country databases even after they have migrated elsewhere. This issue is known as ‘over-coverage’. It can lead to downward bias in the denominators of any rates that we might calculate, as we think that there are more migrants in a host country than there truly are. For outcomes like mortality, over-coverage can also impact the numerator of our rates as not only have migrants exited –while potentially remaining as ‘residents’ in host country data systems – they might well have died elsewhere. This often leads to concerns about whether mortality estimates of migrants can be trusted.

In a recent article investigating the impact of over-coverage on the mortality of migrant populations in Sweden between 2010 and 2015, we built upon the intersection of two recent findings (Wallace and Wilson 2021): first, over-coverage is highest at peak migration ages (ages 15-39), and second, migrant mortality is lowest at these same ages. This led us to wonder whether higher levels of over-coverage at young adult ages are actually driving the lower mortality of migrants at these ages. To answer this question, we used a survival analysis of Sweden’s population registers.

The case of Sweden (consistent with others: U.S., U.K. and France)

As shown in Figure 1, we found a distinct ‘U-shape’ of migrant mortality over age among Sweden’s migrant population. A similar pattern has recently been documented for the migrant populations of the US, the UK, and France (Guillot et al2018), with mortality among migrants relative to the locally-born populations forming a U-shape of lowest-low mortality around peak migration ages. This advantage then disappears, or is reversed, for older migrants, most notably in Sweden. Examining the impact of over-coverage on this ‘U-shape’ of advantage, we found that levels of over-coverage were indeed highest at peak migration ages. We also found that, at some ages, over-coverage may account for a sizeable share of the migrant mortality advantage. Crucially, however, over-coverage in isolation does not explain this lower relative mortality.

For specific origins, both the age-specific pattern of mortality and the impact of over-coverage vary. For example, we found the characteristic U-shape of mortality in some groups (such as Asia, the Middle East, and Central & Eastern Europe) but not in others (such as Finland and the other Nordic countries). Additionally, the impact of adjusting for over-coverage is larger in some groups (such as other Western and other Nordic countries) and much smaller in others (such as the Middle East and for Central & Southern America). Again, however, over-coverage alone does not explain the age variation we observed in the origin-specific mortality analysis.

The lower mortality of international migrants is genuine

Ultimately, we concluded that the unique mortality patterns of international migrants, and in particular their characteristic age profile of mortality, could not be explained by over-coverage, an important potential source of bias in studies that involve migrants. We pointed to migrants born in the Middle East, an origin group that combines the characteristic U-shaped mortality advantage with lower levels of over-coverage, as providing the most reliable evidence to date that the lower mortality of international migrants is genuine.

Given the marked age variation in migrant mortality patterns, we also highlighted the need, where possible, to adopt an age-specific perspective in studies of migrant mortality. Migrants from Central & Eastern Europe exemplify this call, as while young adult migrants in this group have a mortality advantage over the native-born population of Sweden, older migrants have a large disadvantage. We also highlighted migrants from Finland to show that not all migrant groups have an advantage over the native-born population of Sweden. Finnish migrants have a near systematic disadvantage in their mortality levels over age, which are actually underestimated because of population over-coverage.

Research on migrant mortality should refocus attention away from data-related explanations of the advantage and toward understanding the substantive processes that might explain its existence, and the combinations of mechanisms that may result in the absence, reversal, or tapering of these relative advantages with age (see also Ichou and Wallace 2019, Wallace 2019, Wallace and Wilson 2020). Some combination of selection and adaptation is probably at work here, but this is a subject that requires separate investigation.

References

Guillot, M., M. Khlat, I. Elo, M. Solignac, M. Wallace. 2018. Understanding age variations in the migrant mortality advantage: An international comparative perspective, PLoS One13(6): e0199669. doi:10.1371/journal.pone.0199669

Ichou M., Wallace M. 2019. The ‘Healthy Immigrant Effect’: the role of educational selectivity. N-IUSSP, March 10, .

Wallace M. 2019. Low migrant death rates: actual or artefactual? N-IUSSP, April 23.

Wallace M., B. Wilson. 2020. Migrant mortality advantage and the selection hypothesis, N-IUSSP, February 17,

Wallace M., B. Wilson. 2021. Age variations and population over-coverage: Is low mortality among migrants merely a data artefact?Population Studies, online first.

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