A shift away from organized religion appears to be associated with lower birth rates in modern societies, according to new research. An analysis of decades of population data in Finland finds that declines in state church membership are associated with a continued trend in couples having fewer children. The study was published in the journal Social Science Research.
Fertility rates in many high-income countries have fallen to historic lows in recent years. In Finland, the setting for this particular analysis, the total fertility rate fell by 30% between 2010 and 2023. Total fertility rate is a demographic measure that estimates the average number of children a woman will have over her lifetime based on current trends. Declining birth rates can change a society’s economic growth trajectory and lead to an aging population that requires the support of more societal resources than the active workforce.
Researchers wanted to understand exactly what social factors are driving this decline across developed countries. Previous sociological analyzes have linked the historic decline in birth rates to the process of secularization, defined as a society’s gradual move away from religious institutions and values. In particular, little is known about how religion is related to the rapid decline in birth rates seen over the past 20 years. The rapid abandonment of organized religion by younger generations may also be contributing to a similar rapid decline in first-time parents.
Henrik-Alexander Schubert, a demography researcher at the Max Planck Institute for Demographic Research, led the study with colleagues Vegard Skirbeck and Jessica Nissen. The research team proposed that secularization reduces fertility through a dual mechanism. First, there are fewer religious individuals in the overall population, and religious individuals tend to have more children than non-religious people. Second, as the population of religious partners declines, surviving religious individuals are more likely to form partnerships with nonreligious individuals or remain single.
The researchers suspected that this dynamic might reduce the likelihood of childbearing among the remaining religious members of the population. To test this theory, it was necessary to look at the process of family formation from the perspective of the couple, not just the individual. They used Finland, with its highly secularized culture and detailed national record-keeping system, as a testing ground. Although active church attendance is low in Finland, a significant portion of the population maintains membership in the Evangelical Lutheran State Church for cultural or traditional reasons.
To conduct the study, Schubert and colleagues analyzed Finnish administrative registration data covering the period 1995 to 2019. This vast dataset provided a complete record of the registered population residing in the country. To determine religious affiliation, researchers looked at church tax payments. In Finland, members of the national church pay certain taxes based on municipal income, which are automatically collected.
Citizens can officially leave the church by filling out administrative forms or using an online portal, and will be exempt from paying taxes for the following year. Because there is an economic cost to maintaining membership, researchers viewed paying taxes as an objective measure of belonging to an organized religion. They combined these tax records with birth registration and multigenerational data to track the timing and number of births in the population. The final dataset included annual records of childless couples, both married and cohabiting, to see how different combinations of religious affiliation influenced the transition to parenthood.
To ensure consistency, the team controlled for a variety of demographic variables known to influence family planning. They took into account the household income, educational background, and employment status of both partners in a couple. We also accounted for geographic differences by controlling for whether the couple lived in an urban, semi-urban, or rural area.
The researchers found that the birth rate among state church members remained significantly higher than nonmembers throughout the 24-year study period. The mathematical gap between the two groups also widened over time. While the birth rate among the religiously unaffiliated population fell sharply to an average of nearly one child per woman by 2019, the birth rate among the religiously unaffiliated population declined at a much slower pace.
Analyzing the data from the couple’s perspective, the researchers discovered a unique dynamic regarding partner selection. The religious affiliation of male and female partners was correlated with an increased likelihood of having children independently. Most notably, couples in which both partners were members of their state church had the highest rates of first-time parenthood. The combined effect of the two alliance partners was greater than the sum of their individual demographic characteristics.
As the country becomes more secular, the number of religiously homogeneous couples is decreasing. Due to the small number of religious partners available, religious people are increasingly partnering with independents. Such mixed-religion couples have lower birth rates than couples where both partners belong to the church. The researchers suggest that this creates a self-reinforcing downward loop, where a decline in religious affiliation not only reduces the religious population but also suppresses the birthrate of those who maintain their affiliation.
To quantify this impact, the team ran a simulation known as a counterfactual model. This statistical method allowed us to estimate what the birth rate would be if the percentage of church members in the population remained exactly the same as in 2000. Under this simulation scenario, the authors found that the country’s overall fertility rate would have been higher in 2019. The simulations showed that the decline in church membership accounted for a measurable portion of the decline in couples having their first child during the study period.
To eliminate hidden variables, the researchers employed a twin fixed-effects model to compare siblings belonging to different religions. This method helps separate the association between church membership and having children from genetic characteristics and family background. Even after accounting for these family backgrounds, a positive association between church membership and childbearing remained.
The study design included several limitations that limited the generalizability of the findings. Because this study relied on Finland’s state church tax system to measure affiliation, the researchers excluded immigrants who are often members of other religious denominations to which this particular tax does not apply. Furthermore, financial indicators only measure formal organizational affiliation and do not capture the strength of an individual’s religious beliefs or the frequency of their participation in religious services.
Other cultural and economic changes are causing modern birthrate declines worldwide, and the lack of religion is only part of the picture. Economic uncertainty, changes in the housing market, changing personal preferences, and increased instability in relationships are all contributing to declining birth rates across Europe and other high-income countries. The researchers note that their counterfactual simulations showed that secularization directly accounted for only a small proportion of the overall decline.
Future research should investigate whether this relationship between secularization and partner demographics also emerges in other countries without state-sponsored church taxes. Researchers note that assessing the strength of an individual’s religious beliefs can reveal different patterns, particularly regarding gender dynamics. In highly secularized countries, women and men may experience the social aspects of religion differently, which may change the way couples make joint decisions about starting a family.
The study, “Secularization and Fertility Decline: How Declining Church Membership Changes Couples’ Childbearing,” was authored by Henrik-Alexander Schubert, Vegard Skirbeck and Jessica Nissen.
