Political philosophy has developed different conceptions of inequality of opportunity, but empirical research has rarely distinguished between them. A crucial distinction can be made between liberal and radical inequality of opportunity. Liberal inequality of opportunity argues that everyone with the same abilities who makes the same choices should have the same life chances, whereas radical inequality of opportunity regards as unjust the effect on life chances of any factor beyond the individual's control, including her/his abilities. We measure liberal and radical inequality of opportunity in Sweden and obtain precise estimates with minimal measurement error thanks to register data on 740,709 men. We compare liberal and radical inequality of opportunity in six outcomes: education, occupation, income and physical fitness, height, and BMI as measures of health. The results show that the differences between liberal and radical inequality of opportunity are large for education, occupation, income, and physical fitness. For height and BMI, however, there are essentially no differences between liberal and radical inequality of opportunity. With respect to most outcomes, both liberal and radical inequality of opportunity remained rather stable across birth cohorts in Sweden.

Educational choices are heavily stratified by gender. In this study we examine whether an important structural factor in the family of origin, sex composition of the sibling group, affects the emergence of the gender-typed preferences that may drive these choices. Using Swedish population register data, we use multinomial logistic regression models to examine educational choices at upper-secondary school (N = 424,788) and university (N = 133,222) for first-born Swedish men and women in two-child sibling groups, with analyses based on cohorts born 1980–2003. We further examine whether there are any differences in educational choices by parental educational level. We focus on first-born children in two-child families, and we present supplementary analyses for second-born children. We find that men in two-child sibling groups with brothers are more likely to apply for female-dominated upper-secondary programs than men with sisters, while men with sisters are significantly more likely to follow some male-dominated tracks than men with brothers. These differences are concentrated amongst men raised by parents with lower education. However, we do not find that sex composition is associated with university subject choices for men, and we do not find any differences in educational choices for women by the sex composition of the sibling group. These results suggest some support for the predictions that a mixed sex sibling group can lead to a more gender-typed upbringing for men.

Using Swedish register data, this study investigates the association between birth order and upper-secondary school track choice. A large body of research has shown that ordinal position within the sibling group matters for development trajectories and attainment processes. Researchers have also long been interested in the effects of secondary school tracking, showing that it can reinforce the effect of social origins. Using data for over 2 million pupils transitioning from compulsory to non-compulsory upper-secondary school from 1996 to 2019, and sibling fixed-effects, we find that later birth order is negatively associated with the probability of enrolling in university-preparatory academic tracks, known for having higher expected earnings and professional opportunities. These findings persist net of earlier educational performance, gender, parental education, or migration background. Later-born children are more likely to complete vocational programs. These findings shed light on some of the potential mechanisms driving the higher educational attainment, earnings, and employment stability of first- and earlier-born children, as they tend to complete secondary school tracks that provide greater future opportunities. The influence of birth order on completed years of education at age 30 diminishes by half when adjusting for track choices (i.e., secondary effects) and loses statistical significance when GPA (i.e., primary effects) is introduced as an additional control. While an unequivocal explanation for the origins of divergent tracking choices eludes us, existing literature suggests variation in parenting practices, child investments, and the familial environment contribute to these aspirational differences.

Having leadership skills (LS) may increase an individual’s chances of ascending to a higher rank in hierarchical social structures, which can, in turn, provide the resources needed to support a partner and/or a child. Nevertheless, research on the association between LS and family formation processes (marriage, fertility) is scarce. We explore the prospective association between LS and marriage/completed fertility for 650941 Swedish males. Poisson regression and linear probability models are applied, including sibling fixed effects models. Our findings demonstrate a positive association between men’s LS, as measured at the age of assignment to military service (17–20 years), and their probability of marrying by age 39 or older (depending on the birth cohort). Furthermore, among the men in our sample, we find that LS are positively linked with the number of children, and are negatively linked with the probability of remaining childless. These associations are only partially explained by education and income.

STUDY QUESTION: How are the changing maternal age structure and population growth expected to shape future twinning rates in low-income countries? SUMMARY ANSWER: With maternal age at birth projected to shift toward older ages, twinning rates are also estimated to increase in most low-income countries by 2050 and even more by 2100. WHAT IS KNOWN ALREADY: Many of the sub-Saharan African and South Asian countries are undergoing, and projected to further experience, the shift of maternal age at birth to older ages. Advanced maternal age is a well-established predictor of multiple births at the individual level, but currently, it is unknown how the changes in maternal age distribution are associated with the changes in twinning rates at the population level in low-income countries. STUDY DESIGN, SIZE, DURATION: We first estimated age-specific twinning probability based on Demographic Health Surveys and World Fertility Surveys data. We then scaled up the age-specific twinning probability at the population level to estimate changes in the number of twin births in 2050 and 2100 attributable to the estimated shifts in maternal age toward older ages as projected by the UN World Population Prospects (WPP). PARTICIPANTS/MATERIALS, SETTING, METHODS: We analyzed ̴3.19 million births that occurred within 10 years before the interview. Majority of the births in our data took place between 1980 and 2015 across 39 countries, where the uptake of medically assisted reproduction (MAR) is known to have been low during the observation period. We estimated country fixed-effects models to obtain country-specific twinning rates and age-specific twinning probability. We applied these estimates to the future number of births projected by the UN WPP, to estimate the number of twin births in 2050 and 2100. MAIN RESULTS AND THE ROLE OF CHANCE: With maternal age at birth projected to shift toward older ages, twinning rates are also estimated to increase in most countries by 2050 compared to 2010 (increases from 0.3% to 63% depending on countries), and even more in all studied countries by 2100 (increases from 3.5% to 79%). Due to its large population size, India will continue to have among the largest share of twin births despite its estimated decline of twin births by 10.5% by 2100. Nigeria, due to its not only large and growing population size but also high twinning rate, is expected to contribute the second largest number of twin births. LIMITATIONS, REASONS FOR CAUTION: Although the accuracy in maternal recall of multiple births tends to be high, our use of data based on recalled births from the past nonetheless imply a potential bias in our estimation of twinning rates. WIDER IMPLICATIONS OF THE FINDINGS: The present study suggests that, even if the spread of MAR remains slow in many low-income countries, twinning rates and number of twin births are expected to grow as an increase in maternal age at birth and population growth continue. Our findings call for more public health attention and societal support to be paid to twins and their families in low-income countries, given that twins are at higher risk of developmental challenges and health disadvantages. 

An exten sive lit er a ture has exam ined the rela tion ship between birth spac ing and sub se quent health out comes for par ents, par tic u larly for moth ers. However, this research has drawn almost exclu sively on obser va tional research designs, and almost all stud ies have been lim ited to adjusting for observ able fac tors that could con found the rela tion ship between birth spac ing and health out comes. In this study, we use Nor we gian reg is ter data to exam ine the rela tion ship between birth spac ing and the num ber of gen eral prac ti tioner con sul ta tions for moth ers' and fathers' phys i cal and men tal health con cerns imme di ately after child birth (1-5 and 6-11 months after child birth), in the medium term (5-6 years after child bear ing), and in the long term (10-11 years after child bear ing). To exam ine short term health out comes, we esti mate indi vid ual fixed-effects mod els: we hold con stant fac tors that could influ ence par ents' birth spacing behav ior and their health, com par ing health out comes after differ ent births to the same par ent. We apply sib ling fixed effects in our anal y sis of medium- and long-term out comes, hold ing con stant moth ers' and fathers' fam ily back grounds. The results from our ana ly ses that do not apply indi vid ual or sib ling fixed effects are con sis tent with much of the pre vi ous lit er a ture: shorter and lon ger birth inter vals are asso ci ated with worse health out comes than birth inter vals of approx i ma tely 2-3 years. Estimates from indi vid ual fixed-effects mod els sug gest that par tic u larly short inter vals have a mod est neg a tive effect on mater nal men tal health in the short term, with more ambig u ous evi dence that par tic u larly short or long inter vals might mod estly influ ence short-, medium, and longterm phys i cal health out comes. Overall, these results are con sis tent with small to neg li gi ble effects of birth spac ing behav ior on (nonpreg nancyrelated) parental health outcomes.

Despite growing interest in the potential influence of grandparents on grandchild status attainment, research has not addressed whether the ordinal position or number of grandchildren affects outcomes. The authors apply sibling and cousin fixed effects analyses to Swedish population data (cohorts born 1972–2003; 𝑁=2,326,309N=2,326,309), to examine how cousin order and cousin group size influence grade point average (GPA) percentile rank at the end of compulsory school. In sibling fixed effects analyses, second-born, fifth-born, and tenth or later–born maternal cousins achieve GPA ranked scores 0.66, 1.04, and 1.29 percentile points lower than firstborn cousins, respectively. Results for paternal cousins are weaker, suggesting greater influence from the mother’s extended family. In further analyses, the authors examine whether a twin birth to an aunt or uncle has any impact on GPA percentile rank. Instrumental variable analyses indicate that an increase in maternal cousin group size has a statistically significant negative effect on GPA rank at low parities; the effects of an increase in paternal cousin group size are less consistent.

Studies show that body mass index during early adulthood (‘early BMI’) predicts the transition to first birth, but early childbearers tend to be omitted from such studies. This sample selection distorts the prevalence of childlessness, and particularly the racial/ethnic heterogeneity therein, because first birth timing differs by race/ethnicity. We imputed pre-parenthood early BMI for a larger sample, including early childbearers, for the same United States NLSY79 data used in a previous study and simulated differences in the probability of childlessness at age 40+ using posterior distributions based on the Bayesian framework. Obesity was consistently associated with higher childlessness across racial/ethnic groups in both sexes, but only among obese women were first births delayed until after early adulthood. The overall lower childlessness among the underweight women appeared largely driven by Black women. Our findings on the intersectionality of race/ethnicity and sex in the BMI–childlessness pathways encourage research on the underlying mechanisms and on more recent cohorts across different societies. 

Only children (with no full biological siblings) are a growing subgroup in many high-income settings. Previous studies have largely focused on the short-term developmental outcomes of only children, but there is limited evidence on their health outcomes. Using Swedish population register data for cohorts born 1940–75, we compare the health of only children with that of children from multi-child sibling groups, taking into account birth order, family size, and presence of half-siblings. Only children showed lower height and fitness scores, were more likely to be overweight/obese in late adolescence, and experienced higher later-life mortality than those with one or two siblings. However, only children without half-siblings were consistently healthier than those with half-siblings, suggesting that parental disruption confers additional disadvantages. The health disadvantage was attenuated but not fully explained by adjustment for parental characteristics and after using within-family maternal cousin comparison designs.

Although preterm birth is the leading cause of perinatal morbidity and mortality in advanced economies, evidence about the consequences of prematurity in later life is limited. Using Swedish registers for cohorts born 1982-94 (N = 1,087,750), we examine the effects of preterm birth on school grades at age 16 using sibling fixed effects models. We further examine how school grades are affected by degree of prematurity and the compensating roles of family socio-economic resources and characteristics of school districts. Our results show that the negative effects of preterm birth are observed mostly among children born extremely preterm (<28 weeks); children born moderately preterm (32-<37 weeks) suffer no ill effects. We do not find any evidence for a moderating effect of parental socio-economic resources. Children born extremely preterm and in the top decile of school districts achieve as good grades as children born at full term in an average school district.