The More, the Healthier? Effects of Sibling Size on Adolescent Depression in Rural China

INTRODUCTION: Depression in adolescents is of particular concern, given their heightened vulnerability. Previous studies reported mixed findings regarding siblings' role in adolescent mental health, suggesting that sibling effects may be context-dependent. This study investigated how sibling size, an essential aspect of sibling structure, affects adolescent depression in rural China, an area that has experienced both a substantial decline in sibling size and a significant increase in the prevalence of adolescent depression. METHODS: We analyzed longitudinal data from the nationally representative China Family Panel Studies (CFPS, 2010-2022), based on a sample of 16,725 rural adolescents (age: mean = 13.20, SD = 2.34; 46.8% girls). Depression was measured using two scales: the Kessler-6 Rating Scale and the Center for Epidemiologic Studies Depression Scale. An instrumental-variable approach was adopted to address potential endogeneity in sibling size arising from unobservable confounders. RESULTS AND CONCLUSIONS: Our analysis found statistically significant beneficial impacts of sibling size on adolescent mental health. Overall, having an additional sibling lowered one's depression score by 0.11-0.12 SDs and the probability of depression by 1.7-1.8 percentage points. Channel analysis suggested that the enhanced subjective well-being and adaptive behaviors brought by more siblings outweighed the resource-dilution effect, resulting in net mental health benefits. Further heterogeneity analyses revealed that these effects were more pronounced among children in early adolescence (ages 10-13). Moreover, we provided suggestive evidence of heterogeneity in sibsize effects across sibling structure.