The PHDCN began in the mid-1990s to study individual lives within their social contexts, focusing on neighbourhoods, families, peers, schools, and the criminal justice system. It involved a broadly representative sample of over 6,200 children and adolescents from Chicago, United States, drawn from a screening of more than 35,000 households across 80 neighbourhoods. The children in the cohort fall into seven age cohorts including infancy, and then every 3 years until age 18 (i.e., age 3, 6, 9, 12, 15, and 18).