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

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.

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.

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.