Educational disparities in cohort fertility rates (CFR) often serve as the starting point for analyzing socioeconomic drivers of fertility. As most children are born to couples, the relationship between education and fertility is the compound of both partners’ education. Measuring both partners' educational levels is generally considered superior to measuring one partner’s educational level. Yet, no study has comprehensively analyzed cohort fertility by couple’s educational pairing. Using Finnish register data, we provide the first analysis of CRFs from the perspective of educational pairings. For the female birth cohorts of 1969 -1975, we decompose the CFR from births by the educational pairing of the union in which they occur. This novel measure complements previous work focusing on the incidence or instantaneous birth risks by educational pairing, as it draws on lifetime exposure to unions by educational pairings and birth rate within such unions. Our analysis reveals that the CRF in Finland— for the most recent cohorts from which such measures can be derived— is predominantly the result of births in educationally hypogamous or homogamous unions, and unions where at least one partner has tertiary education. In particular, the CFR of highly educated women is composed of births to highly educated partners.

Recent period trends in the Nordic countries show rapid declines in first births, particularly amonglower-educated men and women. This study translates these period changes into cohort patterns andanalyzes observed and forecasted ultimate childlessness by education for men and women born1970–1987/88 in Denmark, Finland, Iceland, Norway, and Sweden using register-based data. Weapply three forecasting methods: freeze rates, five-year extrapolation, and a nonparametric approachbased on historical first-birth probabilities. Results reveal the steepest increases in ultimatechildlessness among the lowest educated, approaching as high as 40% among low-educated womenand 50% among low-educated men in some of the countries. Among the higher tertiary educated,childlessness is overall lower and remains relatively stable. By contrast, men with lower tertiaryeducation show notable increases in childlessness, in some cases reaching levels similar to or higherthan those of upper-secondary-educated men. While overall childlessness in Denmark remainsstable, it exhibits the fastest widening educational gap. These findings underscore a growingeducational polarization in the transition to parenthood across the Nordic societies, with women’schildlessness patterns increasingly resembling those of men—a marked shift in the region’s fertilitylandscape.

ObjectiveThis study analyzes heterogeneity in divorce rates after the 1987 transition from mutual consent to unilateral no-fault divorce in Finland.BackgroundMarriage and divorce legislation can impact divorce rates. However, some groups may be more responsive to changes in legal context than others. We propose that unilateral no-fault divorce laws either (a) increase divorce more in more or less divorce-prone groups, or (b) increase divorce equally across these groups.MethodsWe use population-wide individual-level register data from Finland to identify salient social groups with different divorce propensity, including ethno-linguistic and religious affiliations with divergent divorce propensity and couples of different parental status, marriage length, and marital history. We use piecewise constant exponential survival models to estimate the association with divorce proneness before and after the introduction of mutual consent divorce laws.ResultsDivorce rates increase in all studied subgroups by about 60% in the years following unilateral divorce. We found no support for the hypothesis that groups that were either more or less divorce-prone prior to the reform would be particularly responsive to divorce liberalization in the short-to-medium term.ConclusionsThe findings speak toward a universal rather than heterogeneous effect of divorce law liberalization.

Bateman's principles heavily influence the understanding of human reproductive behaviour. Yet, few rigorous studies on Bateman's principles in contemporary industrialized populations exist. Most studies use small samples, exclude non-marital unions, and disregard recent insights on within-population heterogeneity in mating strategies. We assess mating success and reproductive success using population-wide Finnish register data on marital and non-marital cohabitations and fertility. We examine variability across social strata in the Bateman principles and analyse the mate count, the cumulated duration with a mate, and the association with reproductive success. Results support Bateman's first and second principles. Regarding Bateman's third principle, the number of mates is more positively associated with reproductive success for men than women, but this association is driven by ever having a mate. Having more than one mate is on average associated with lower reproductive success. However, for men in the lowest income quartile, having more than one mate positively predicts reproductive success. Longer union duration is associated with higher reproductive success, and more so for men. We note that sex differences in the relationship between mating success and reproductive success differ by social strata, and argue that mate duration may be an important component of mating success alongside mate count.

The influence of kin on various outcomes is heavily debated. However, kinship size itself conditions the probability of potential effects. Socio-economic gradients in the prevalence, variance, and types of kin are, therefore, a vital aspect of the functions of kin. Unfortunately, these parameters are largely unknown. We used Swedish register data to enumerate consanguine and in-law kin across the life course of the 1975 birth cohort. We calculated differences in kinship size between this cohort's income quartiles and educational groups. We decomposed how specific kin relations, generations, and demographic behaviours contributed to these differences. Among low socio-economic status (SES) groups, higher fertility in earlier generations resulted in more kin compared with high-SES groups. Low-SES groups had more horizontal consanguine kin, while high-SES groups had more in-laws. Lower fertility and higher union instability among low-SES men substantially narrowed SES differences in kinship size. Kinship size varied substantially within SES groups.

Individuals increasingly enter a series of relationships during their reproductive years. As births in higher-order unions increase, fertility becomes partially contingent on re-partnering. Previous research suggests that men re-partner at higher rates than women. This study analyzes whether gender differences in partnering and re-partnering influence gender differences in cohort fertility. We use Finnish register data on all births, marriages, and cohabitations between the ages of 18 and 47 over four full birth cohorts. The gender differences in cohort fertility rate are decomposed into components due to birth rate differences and a compositional component owing to gender differences in the share partnered and re-partnered. We observe no impact of “re-partnering premium” on male fertility. Men have marginally higher re-partnering rates at older ages, when birth rates are low, whereas women have higher rates of partnering and re-partnering at prime childbearing ages. This compositional effect drives a “partnering” advantage for female fertility. This connection between gender differences in partnering and cohort fertility is true across educational levels.

Given that surprisingly little is known about the demography of human kinship, we provide a demographic account of the kinship networks of individuals in Sweden in 2017 across sex and cohort between ages 0 and 102. We used administrative register data of the full population of Sweden to provide the first kinship enumeration for a complete population based on empirical data. We created ego-focused kinship networks of children, parents, siblings, grandchildren, grandparents, aunts and uncles, nieces and nephews, and cousins. We show the average number of kin of different types, the distribution of the number of kin, and changes in dispersion over time. A large share of all kin of an individual are horizontal kin, such as cousins. We observe the highest number of kin-on average, roughly 20-around age 35. We show differences between matrilineal and patrilineal kin and differences in the kinship structure arising from fertility with more than one childbearing partner, such as half-siblings. The results demonstrate substantial variability in kinship within a population. We discuss our findings in the context of other methods to estimate kinship.

BACKGROUNDThe decline in marriage and increase in cohabiting unions represent a major change in family and fertility dynamics. Yet, no comprehensive description has covered period trends in the prevalence of marital and non-marital partnerships, or partnership entry and exit rates, across educational levels.OBJECTIVEWe describe period trends in the proportion of partnered individuals and the flow of partnership formation and dissolution at ages 18–49 across educational levels for men and women in 1989–2019 in Finland.METHODSWe use total-population register data that include full histories of co-residential partnerships regardless of marital status. We calculate the age-specific yearly prevalence of marriages, cohabitations, and all unions; and rates of union formation (among non-partnered population) and rates of separation (among the partnered population).RESULTSThe prevalence of marriage declined across educational groups. Increases in the prevalence of cohabitation are slightly smaller than declines in marriage; as a result, the total prevalence of partnerships declined, especially among low-educated men and women. Union formation rates have declined recently, and separation rates have increased notably, but more so among the lower educated and in age groups below 35.CONCLUSIONSThe increase of non-marital cohabitation has not fully covered for the decline in marriage. Increases in partnership instability are notable. All partnership trends and the educational gradients are remarkably similar among men and women in Finland.CONTRIBUTIONWe provide the first comprehensive population-level estimates of trends and patterns of the partnership stock and flows of marital and non-marital partnerships by education for both men and women.

Partnering behavior is central to understanding fertility. Influential concepts, including singlehood, serial monogamy, and multiple‐partner fertility, are frequently used to analyze partnering and childbearing dynamics. These concepts are evoked to understand individual and population‐level patterns but are mainly analyzed at the individual level. We propose a measure for gauging the interplay between partnerships and childbearing at the population level, namely cohort fertility rates (CFR) as the sum of births under various partnership contexts. Surprisingly, demographers rarely measure and do not have a clear picture of the extent to which childbearing in different partnership contexts contributes to completed fertility. We analyze Finnish register data to decompose CFR into births across union status, union order, and reproductive partner order. Contrary to the discourse of partnering in the Nordics, births within first unions to first reproductive partners account for about two‐thirds of CFR. Births in higher‐order unions to first reproductive partners account for one‐fifth. Single births and births with higher‐order reproductive partners have a modest impact. This ranking holds across sex and educational level. We argue that the proposed measures offer a novel appraisal of population‐level implications of partnerships and childbearing dynamics and provide an opportunity to understand cross‐country variation in fertility patterns.

Partnering behavior is central to understanding fertility. Influential concepts, including singlehood, serial monogamy, and multiple-partner fertility, are frequently used to analyze the interplay between partnering and fertility at the individual level. However, these frameworks are also evoked to understand population-level patterns. One fundamental population-level pattern for gauging the relationship between partnerships and childbearing, we argue, is the enumeration of fertility as the sum of births under various partnership conditions. Surprisingly, demographers rarely measure and have not yet a clear picture of the extent to which childbearing in different partnership contexts contributes to completed fertility. We analyze Finnish register data to decompose the cohort fertility rate (CFR) into births from eight partner contexts, in conjunction with three dimensions: union status, union order, and reproductive partner order. Somewhat contrary to discourse of partnering in the Nordics, we conclude that births within first unions to first reproductive partners account for two-thirds of CFR. Births in higher-order unions to first reproductive partners account for one-fifth. Single births and births with higher-order reproductive partners have a modest impact. This ranking holds across sex and educational level, with substantive relative differences. We argue that these descriptions provide an additional perspective to appraise childbearing and partnering dynamics.

Extensive literature theorizes the role of re-partnering on cohort fertility and whether union dissolution can be an engine for fertility. A large share of higher-order unions is non-marital cohabitations. Yet, most previous completed cohort fertility studies on the topic analyze marital unions only and none have measured cohabitations using population-level data. We use Finnish register data to enumerate every birth, marriage, and cohabitation from ages 18-46 in the 1969–1972 birth cohorts, and analyze the relationship between the number of unions and cohort fertility for men and women using Poisson regression. We show that re-partnering is driven by cohabitations. Re-marriage is positively associated with cohort fertility, compared to individuals in a single intact marriage. However, when measured using marriages as well as non-marital cohabitations, re-partnering is negatively associated with fertility, compared to individuals in a single intact union. This negative association increases with socioeconomic status. “Serial cohabitation” is a strong predictor of low fertility. Men see a slight “re-marriage premium” in fertility and a (non-marital) “re-partnering penalty,” compared to women. Thus, re-partnering is likely not an efficient engine for fertility. Further, marriage and cohabitation are far from indistinguishable in a country often described as a second demographic transition forerunner.

An extensive literature theorizes the role of repartnering for cohort fertility and whether union dissolution can be an engine for fertility. A large share of higher order unions are nonmarital cohabitations, but most previous studies on completed cohort fertility have analyzed only marital unions, and none have incorporated nonmarital cohabitations using population-level data. To analyze the relationship between the number of unions and cohort fertility for men and women, we use Poisson regression with Finnish register data to enumerate every birth, marriage, and cohabitation among the 1969-1972 birth cohorts at ages 18-46. We show that dissolutions of first cohabitations are the main pathway to repartnering and that most higher order unions are cohabitations. Nonmarital repartnering is a strong predictor of low fertility. In contrast, remarriage is positively associated with cohort fertility. Because the bulk of first-union dissolutions and higher order unions are nonmarital, repartnering is not an efficient engine for fertility at the aggregate level. Marriage and cohabitation are far from indistinguishable in a country often described as a second demographic transition forerunner.

Socioeconomic status influences demographic behavior. Moreover, socioeconomic status tends to correlate across generations. Consequently, kinship structures likely display social stratification. However, the processes of kinship stratification are intricate, and its prevalence and antecedents are rarely studied empirically. We have estimated socioeconomic differences in kinship in Sweden using administrative register data of the total Swedish population. We created kinship networks for the 1973 birth cohort and followed the growth and decline of kin from birth to age 45 of this birth cohort. We analyzed consanguineous kin, as well as spouses, reproductive partners, parents-in-law, and siblings-in-law. We calculated the difference in total kinship size across earnings and educational groups. We broke down the contributions of specific kin groups to this difference and also analyzed which demographic behaviors and generations contributed most to socioeconomic differences in kinship. Among men and women with low socioeconomic status (SES), higher fertility in earlier generations resulted in more kin than those with high SES. Among low SES men and siblings, lower fertility and union instability narrowed SES differences in the number of kin.

Dear Editor, For physicians who wish to have children, their choice of partner might impact work hours [1, 2], career decisions [1-3], time spent caring for children [2] and relationship satisfaction [4]. As such, purported increases in dual physician households [2, 3] or medical marriages [4] (physicians who partner with other physicians; a phenomenon called endogamy [5]) have been subject to much attention. However, data on physicians’ partners from population-based samples are scarce and trends over time in physician partner choice have not been assessed. We used nationwide administrative registers in Sweden (described in Supporting Information Appendix), including the total population register and educational registers. We included physicians, born between 1941 and 1975, who had completed their medical education or had their medical qualifications registered in Sweden by age 42. We identified all individuals with whom the physicians had at least one child through age 42, based on all childbearing events, including biological (live births) or adopted children. We categorized physicians into 5-year birth cohorts and described the 10 most common educational fields (focus of educational program) [6] of physicians’ partners, using categories described in Table S1. Analyses were performed by sex using Stata version 16.1 (StataCorp). The Regional Ethics Committee in Stockholm, Sweden, approved the study. Analyses included 16,385 female physicians and their 14,024 partners and 21,300 male physicians and their 18,415 partners. The number of male physicians varied by birth cohort with no apparent trend over time. The number of female physicians had increased across birth cohorts (Table S2). Figure 1 shows the 10 most common educational fields of partners to physicians born in 1941–1945, 1956–1960 and 1971–1975 (Tables S3 and S4 show data for all birth cohorts). Female physicians most commonly partnered with physicians (22.9% of partners) and engineers (15.7%). This was consistent across birth cohorts, although the proportion who were physicians had increased slightly from 19.9% to 25.9% among partners to female physicians born between 1941 and 1945 versus 1971 and 1975. Male physicians most commonly partnered with physicians (18.4%), nurses (18.1%) and teachers (15.3%). When comparing partners to male physicians born between 1941and 1945 versus 1971 and 1975, the proportion who were teachers had decreased from 22.6% to 9.3%, and the proportion who were nurses had decreased from 19.3% to 11.8% while the proportion who were physicians had more than doubled, from 12.0% to 29.8%. Female physicians in Sweden born between 1941 and 1975 most commonly partnered with engineers and physicians for their childbearing unions; this tendency remained consistent across birth cohorts, although the proportion of partners who were physicians had increased slightly. Male physicians born in 1941–1960 most commonly partnered with teachers or nurses; this later changed to physicians among those born in 1961–1975, with this coinciding with an increased number of female physicians in the country. Of the partners to both female and male physicians born in 1971–1975, nearly 30% were physicians. While the purported increase in “dual physician households” has received much attention in recent medical literature [2, 3], such an increase had occurred predominantly among male physicians in our study; for female physicians, partnering with another physician had been common for decades. While our study is limited to physicians in Sweden, our findings align with studies from various populations and birth cohorts showing that highly educated women in heterosexual relationships, on the group level, tend to partner with men of equal or higher education or income, with this inclination being attributed to both preference and availability [7]. In contrast, partner choice of highly educated men tends to vary more significantly [7-9]. Moreover, in accordance with our findings, analyses of 25- to 50-year-old physicians in a US nationally representative survey (2000–2015) [1] showed that 31.4% of married female physicians and 17.1% of married male physicians had partnered with physicians. Our analyses used nationwide register data (rather than survey data) with nearly complete coverage with respect to educational characteristics and partners for childbearing unions, also included unmarried physicians, assessed partners with whom physicians had children (rather than marriage), examined changes over time and provided data also on partners who were not healthcare professionals. Our analyses only accounted for childbearing unions that were captured in the administrative registers: registration of same sex childbearing unions started in 2005. To ensure comparability across birth cohorts, we did not include childbearing events occurring after age 42; however, vital statistics show that almost all women and around 94% of men who had children did so before age 40 [10]. Partner occupation (and income) could affect decisions that influence career progression [1-3] and work–life balance such as within-couple distribution of parental leave and childbearing responsibilities [2]. The convergence of male and female physicians’ partner choice and its implications for physicians’ personal and professional lives merit further examination. None. The authors declare no conflict of interest. Linus Andersson had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Concept and design: Linus Andersson, Margarita Chudnovskaya and Peter Ueda. Acquisition, analysis, or interpretation of data, and critical revision of the manuscript for important intellectual content: All authors. Drafting of the manuscript: Linus Andersson, Margarita Chudnovskaya, Cyrus Ghaznavi and Peter Ueda. Statistical analysis: Linus Andersson and Peter Ueda. None. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Individuals increasingly transition through more than one cohabiting relationship during their reproductive years. Therefore, births often occur after the dissolution of a first union. Previous research suggests that men and women differ in their re-partnering patterns, and has often found a re-partnering advantage for men. This study analysed the role of sex differences in re-partnering for sex differences in total fertility achieved after first union dissolution. We use Finnish register data to separately document all marital and cohabiting unions and all births which occur after the first union dissolution of four full birth cohorts up to age 48 for men and women. We decompose the sex difference in the summed fertility occurring after the first union dissolution up to age 48 into two parts: one rate component owing to sex differences in birth rates and a compositional component owing to sex differences in the share in re-partnered unions. On average, the post-dissolution fertility of women was higher than that of men. Women see a re-partnering advantage at early ages, while men have a re-partnering advantage at later ages. Tertiary educated men who dissolve a first childbearing union have higher post-dissolution fertility than their female counterparts and, for this group, a male ‘re-partnering advantage’ across the life course accounts for a substantial part of this sex difference.

Bateman’s principles continue to influence the understanding of human reproductive behaviour despite enduring criticism. However, few rigorous studies on Bateman’s principles in contemporary industrialized populations exist, and previous studies are hampered by small sample size and exclusion of non-marital unions. Here we address these shortcomings by assessing mating success and reproductive success using population-wide Finnish register data of marital and non-marital co-habitations and children born. These unique data allow us to compare different operationalizations of mating success, namely, co-residential unions and cumulated union duration; and to examine variability across social strata. Our data support Bateman’s first and second principles but the association between mating success and reproductive success is less clear. The number of unions is somewhat more positively associated with reproductive success for men than women, and the mating success–reproductive success association turns negative when adjusting for union duration. Having had more mates is associated with lower reproductive success than having had one union. More unions are positively associated with higher reproductive success only for men in the lowest income quartile. We conclude that union duration, controlling number of unions, is associated with higher male reproductive success and should be incorporated as an important dimension of mating success.

Most research on trends in socioeconomic fertility differences focus on cohort total fertility. This study asks how cohort trends in parity-specific fertility differ across educational segments for men and women, and what role multi-partner fertility plays in these trends. The study used Finnish and Swedish register data on cohorts born in 1940–1973/1978. The main analyses use parity progression ratios. Ordinary ratios were contrasted with ratios on births to first reproductive partner. Among lowand medium-educated persons we observe parity polarization, where both childlessness and higher parity (3+) births increase, largely reflecting increases in multi-partner fertility. Highly educated men and women more often have exactly two children. We demonstrate that cohort total fertility can mask significant parity-specific trends across educational groups, and that changes in multi-partner fertility can be a part and parcel of cohort trends in socioeconomic fertility differentials.

The proportion of life spent caring for dependent children is a defining feature of life courses. This study uses Swedish register data to analyze the period of life spent as parents to children no older than 18 as a salient difference between single- and multiple-partner fertility trajectories. Individuals who have children with more than one partner spend a much longer time as parents to dependent children than those who have children with one partner, on average 8.2 more years among men and 6.2 more years among women. Cross-partner birth spacing is a more powerful proximate cause of this gap than completed fertility. We argue that an extended time parenthood is part and parcel to multi-partner fertility and discuss implications of this.

This paper estimates the size of the effect of parental union dissolution on offspring union dissolution, as a share of the sum of all social origin factors. A large literature has documented a positive correlation between divorce and separation among parents and their children. Parental union dissolution is one out of several aspects of social origin that is associated with union dissolution. It is difficult to contrast the relative impact of parental union dissolution to other aspects of social origin because many apects of social origin are unobservable. Swedish administrative data for the 1960 to 1965 birth cohorts that cover the individuals’ life events until 2018 is used to estimate sibling correlations in divorce and childbearing union dissolution, adjusting for parental union dissolution. The variance in union dissolution attributable to factors shared by siblings ranged from 6% to 13%. Parental union dissolution and factors associated with parental union dissolution explained between 15% and 28% of this variance. Sister correlations are greater than brother correlations, and sibling correlations of childbearing union dissolution are higher than sibling correlations of divorce. It is pertinent to estimate the total effect of all social background factors on offspring union dissolution. It is likewise of interest to specify the share of all social background effects that are constituted by factors caused by or correlated specifically with parental union dissolution. Sibling correlations can be a useful tool for quantifying these relationships.

BACKGROUND Research indicates that both full- and half-siblingships develop enduring social relationships, if the siblings have the opportunity to interact during childhood and adolescence. OBJECTIVE To estimate: (1) how much time half- and full-siblings are exposed to each other during childhood and adolescence; (2) how half-sibling exposure is conditional on birth spacing and residency; and (3) how parents' social vulnerability is associated with different levels of lifetime exposure to half-siblings. METHOD Swedish register data is used to calculate exposure to half-siblings based on birth spacing and registered residency for all full- and half-siblings in the 1994 birth cohort. RESULTS A substantive share of half-siblings are less exposed to each other due to lengthy birth spacing and residency patterns. By age 18, 26% of the birth cohort have had a half-sibling who is also no older than 18 for at least one year; 13% of the birth cohort have had a half-sibling who is no older than 18 for up to 10 years; 8% of the birth cohort have been registered in the same dwelling as another half-sibling for eight years or more. Parents' social vulnerability does not predict exposure to halfsiblings among the population that has at least one half-sibling by age 18. CONCLUSION Even though half-siblings constitute a large share of all siblings, full-siblings will likely make up the vast majority of the siblingship-like relationships because so many halfsiblings are unable to interact during childhood or adolescence due to extensive age differences and/or because they do not coreside.