Understanding Heterogeneity in the Effects of Birth Weight on Adult Cognition and Wages

Jason Fletcher, University of Wisconsin-Madison
Justin Cook, Yale University

Research has documented long term impacts of birth weight on adult outcomes, including IQ and earnings. The effects are often robust to sibling or twin fixed effects. We examine potential mechanisms underlying these effects by incorporating findings from the genetics and neuroscience literatures. We use a sample of siblings combined with an“orchids and dandelions hypothesis”, where the IQ of genetic dandelions is not affected by in utero nutrition variation but genetic orchids thrive under advantageous conditions and wilt in poor conditions. Indeed, using variation in three genes related to neuroplasticity (APOE, BDNF, and COMT), we find substantial heterogeneity in the effects of birth weight on adult outcomes, where part of the population (i.e., “dandelions”) is not affected by birth weight variation. Our results help uncover why birth weight affects adult outcomes and also point to the benefits of targeting interventions to individuals susceptible to the impacts of low birth weight.