Sibling-sex effects on voter turnout

In this study, we examine how one aspect of sibling relations—the sex of one’s sibling—affects voter participation. To credibly identify causal effects, we focus on spillover from having a younger sibling of a given sex. Drawing on Swedish population registers and validated turnout data from seven national and European Parliament elections between 1982 and 2022, we show that having a same-sex sibling increases the likelihood of voting among women, but less so among men. Our supplementary analyses provide suggestive evidence that closer sister-to-sister ties, combined with women’s higher propensity to vote, partly explain the observed effects. Taken together, these findings broaden our understanding of how the family context shapes political participation and point to sibling relations as an underappreciated force behind electoral behavior. While much remains to be learned about the political consequences of sibling dynamics, our results suggest that who we grow up with—even something as seemingly simple as a sibling’s sex—can leave a lasting mark on our democratic engagement.