No Evidence That Siblings’ Gender Affects Personality Across Nine Countries

No Evidence That Siblings’ Gender Affects Personality Across Nine Countries. Thomas Dudek et al. Psychological Science, August 23, 2022. https://doi.org/10.1177/09567976221094630

Abstract: Does growing up with a sister rather than a brother affect personality? In this article, we provide a comprehensive analysis of the effects of siblings’ gender on adults’ personality, using data from 85,887 people from 12 large representative surveys covering nine countries (United States, United Kingdom, The Netherlands, Germany, Switzerland, Australia, Mexico, China, and Indonesia). We investigated the personality traits of risk tolerance, trust, patience, locus of control, and the Big Five. We found no meaningful causal effects of the gender of the next younger sibling and no associations with the gender of the next older sibling. Given the high statistical power and consistent results in the overall sample and relevant subsamples, our results suggest that siblings’ gender does not systematically affect personality.

Keywords: personality, siblings, gender, open materials

Discussion

Overall, we conclude that siblings’ gender does not meaningfully affect personality. Although data came from only nine countries (with a predominance on Western countries), the consistently small associations challenge the notion that any type of universal, gendered sibship dynamics affects personality. This conclusion also aligns with recent findings suggesting that one’s ordinal position among siblings does not meaningfully affect personality (Botzet et al., 2021; Damian & Roberts, 2015b; Lejarraga et al., 2019; Rohrer et al., 2015, 2017). Of course, it is possible that the effects of siblings’ gender and birth-order position are even more subtle and thus not detectable even when very large samples are investigated. This interpretation would align with recent suggestions that environmental influences, just like genetic influences, may be driven by thousands of factors, each with very small effect sizes (von Stumm & d’Apice, 2022). However, taking findings from behavioral genetics into account, it seems like these environmental causes are more likely to be found outside of the family environment (Briley & Tucker-Drob, 2014; Vukasović & Bratko, 2015).

It is also possible that the proposed mechanisms of both social-learning and sibling-differentiation theory apply in varying degrees in different families, resulting in average effects that net out at zero but that may occasionally “show up” in individual studies as significant effects. However, this account does not provide the most parsimonious explanation for discrepancies between our study and the past literature on the topic. Given inconsistent methodologies and small sample sizes, it seems reasonable that at least some of the incoherence can be attributed to publication bias (Ioannidis, 2005), which can result in a “continuous stream of conflicting results” (Damian & Roberts, 2015a). Furthermore, both social learning and sibling differentiation suggest that the effects of siblings’ gender are mediated through siblings’ personality—but the link between gender and personality is only of medium strength in the first place, even when an index designed to maximize differences is used. Thus, large effects of sibling gender may be implausible to begin with.

Lastly, sibling gender may not affect the widely used broad personality measures that we investigated, but recent economic research suggests that it does affect important life outcomes. Findings suggest that brothers decrease women’s labor earnings and that this may be partly driven by increased traditional family attitudes (Brenøe, 2022; Cools & Patacchini, 2019; Rao & Chatterjee, 2018). Investigating the specific mechanisms behind this brother-earnings penalty—whether they are psychological, sociological, or economic in nature—seems a worthwhile research endeavor. Our findings suggest that personality differences do not play a major part in this story.