and sociometric ratings of the entire population at those sites. The original CDP sample consisted of 585 children (52% male; 81% European American, 17% African American, and 2% belonging to other ethnic groups). More than 20% of participants were born into single-parent families, and more than half lived with single or divorced parents before adulthood. Data collection began the summer before the participants entered kindergarten (at about 5 years of age) and follow-ups have been conducted annually and remain ongoing. Through newsletters, birthday cards, handwritten thank-you notes, postmaster notification of changed addresses, tracking through named relatives and friends, and Web-based searches, we have maintained high rates of participation over time. Ninety percent (n=526) of the original 585 participants took part in at least 1 assessment in early adulthood (ages, 19-23 years). The 10% that attrited had been slightly higher in kindergarten teacher–reported externalizing behavior and lower in socioeconomic status than the retained sample, but the groups did not differ in other measures, including ethnicity. We have routinely tested for site and cohort (1987 vs 1988) main effects and interactions, but none of these tests yielded significant site or cohort effects.
