One to one matching to cocaine dependent cases based on year of birth (within 1 year), gender, ethnicity, and neighborhood (using zip code) was employed to recruit community-based comparison participants. Potential participants were identified through the Missouri Family Registry maintained by Washington University in St. Louis for research purposes. This registry includes all Missouri residents who have a driver’s license or state identification card (i.e., non-drivers). Individuals were sent a letter describing the study, followed by a phone call inviting them to participate. Year of birth, gender, and ethnicity were confirmed during telephone screening. The community-based individuals were also required to have a full sibling within five years of their age who was willing to participate. Eighty percent of screened and eligible community recruited individuals participated. Substance dependence and other psychiatric disorders were not exclusionary criteria for community-based participants.
