Observing many researchers using the same data and hypothesis reveals a hidden universe of uncertainty.

This study explores how researchers' analytical choices affect the reliability of scientific findings. Most discussions of reliability problems in science focus on systematic biases. We broaden the lens to emphasize the idiosyncrasy of conscious and unconscious decisions that researchers make during data analysis. We coordinated 161 researchers in 73 research teams and observed their research decisions as they used the same data to independently test the same prominent social science hypothesis: that greater immigration reduces support for social policies among the public. In this typical case of social science research, research teams reported both widely diverging numerical findings and substantive conclusions despite identical start conditions. Researchers' expertise, prior beliefs, and expectations barely predict the wide variation in research outcomes. More than 95% of the total variance in numerical results remains unexplained even after qualitative coding of all identifiable decisions in each team's workflow. This reveals a universe of uncertainty that remains hidden when considering a single study in isolation. The idiosyncratic nature of how researchers' results and conclusions varied is a previously underappreciated explanation for why many scientific hypotheses remain contested. These results call for greater epistemic humility and clarity in reporting scientific findings.

Fertility Intentions and Their Realization in Couples: How the Division of Household Chores Matters.

Most research on Europe indicates that a gender-balanced division of family work tends to increase childbearing probabilities, but empirical results vary substantially. The present article proposes explanations for this observed discrepancy. It develops prior research further by (1) studying short-term fertility intentions and their realization within the subsequent 4 years, (2) analyzing the role of the spouses' satisfaction with the division for the effects that the division may have on childbearing, (3) proving a mediation by relationship satisfaction, and (4) considering gender as well as parity as moderators. Using data from two waves of the Generations and Gender Survey, we show that the division of work affects childbearing intentions. We find that the effect (a) depends on the spouses' satisfaction with the division, (b) is partly moderated by relationship satisfaction, and (c) varies by parity. The division of household labor, however, seems of less importance for the realization of childbearing intentions.

Seeding the gender revolution: Women's education and cohort fertility among the baby boom generations.

In Europe and the United States, women's educational attainment started to increase around the middle of the twentieth century. The expected implication was fertility decline and postponement, whereas in fact the opposite occurred. We analyse trends in the quantum of cohort fertility among the baby boom generations in 15 countries and how these relate to women's education. Over the 1901-45 cohorts, the proportion of parents with exactly two children rose steadily and homogeneity in family sizes increased. Progression to a third child and beyond declined in all the countries, continuing the ongoing trends of the fertility transition. In countries with a baby boom, and especially among women with post-primary education, this was compensated for by decreasing childlessness and increasing progression to a second child. These changes, linked to earlier stages of the fertility transition, laid the foundations for later fertility patterns associated with the gender revolution.

The limited effect of increasing educational attainment on childlessness trends in twentieth-century Europe, women born 1916-65.

During the twentieth century, trends in childlessness varied strongly across European countries while educational attainment grew continuously across them. Using census and large-scale survey data from 13 European countries, we investigated the relationship between these two factors among women born between 1916 and 1965. Up to the 1940 birth cohort, the share of women childless at age 40+ decreased universally. Afterwards, the trends diverged across countries. The results suggest that the overall trends were related mainly to changing rates of childlessness within educational groups and only marginally to changes in the educational composition of the population. Over time, childlessness levels of the medium-educated and high-educated became closer to those of the low-educated, but the difference in level between the two better educated groups remained stable in Western and Southern Europe and increased slightly in the East.

Assessing Short-Term Fertility Intentions and Their Realisation Using the Generations and Gender Survey: Pitfalls and Challenges.

The use of fertility intention questions to study individual childbearing behaviour has developed rapidly in recent decades. In Europe, the Generations and Gender Surveys are the main sources of cross-national data on fertility intentions and their realisation. This study investigates how an inconsistent implementation of a question about wanting a child now affects the cross-country comparability of intentions to have a child within the next three years and their realisation. We conduct our analysis separately for women and men at prime and late reproductive ages in Austria, France, Italy and Poland. The results show that the overall share of respondents intending to have a child at some point in their life is similar in all four analysed countries. However, once the time horizon and the degree of certainty of fertility intentions are included, substantial cross-country differences appear, particularly in terms of proceptive behaviour and, consequently, the realisation of fertility intentions. We conclude that the inconsistent questionnaire adaptation makes it very difficult to assess the role of country context in the realisation of childbearing intentions.

Didn't Plan One but got One: Unintended and sooner-than-intended Parents in the East and the West of Europe.

The realisation rates of short-term childbearing intentions are known to be consistently lower in post-socialist countries than in the rest of Europe. However, the East-West differences in the outcomes of intentions to postpone or forego (further) childbearing have not been previously examined. We employ two panel waves of the Generations and Gender Survey in six countries (three from Eastern and three from Western Europe), and, based on the short- and long-term fertility intentions expressed by respondents at the first survey wave, we classify the births occurring between two waves as intended, sooner-than-intended, or unintended. We find that in our study population of non-teenage respondents who had the same partner at both survey waves and a child between the two survey waves, between around 10% (Western European countries) and 30% (Eastern European countries) experienced an unintended or a sooner-than-intended birth. The East-West divide is largely driven by the share of unintended parents which is clearly higher in the post-socialist countries. However, the geographical pattern fades away once we control for the anticipated costs of having a child. Our study gives insight into East-West differences in attitudes to childbearing and into how they affect reproductive behaviour. It also offers methodological improvements of cross-national panel surveys designed to examine childbearing intentions that would allow for a more accurate assessment of childbearing intendedness.