The effect of sibship size on non-cognitive Skills: Evidence from natural experiments

A large literature has documented how families shape the developmental trajectories of children. While the formation of socio-emotional and non-cognitive traits, like personality, are driven by both genetic and environmental factors, much of the variation in these traits is unexplained. Economic and psychological models of personality formation suggest an important role for family interactions and dynamics, though much of the research has focused on parental time and financial resources and has not yet focused attention on the potential importance of sibling interactions. Siblings could have a negative effect on children's development if they are in competition for household resources but could have a positive effect if they provide opportunities for beneficial interactions, behavior modeling, and kin care. The net effect of these processes on children's personality development is an empirical question. We used data from Add Health to examine causal effects of having additional siblings on adult personality traits. We deploy two analytic aims within a “natural experiment” empirical design that use the birth of twins in the household to estimate sibling effects. Using both intent-to-treat and instrumental variables research designs we report large (0.5–1.5 standard deviation) differences in adult personality of those who have an additional younger sibling in the household during childhood. These differences likely create labor market and life course disadvantages for children with larger sibships.