Screening calls made to twins queried their willingness to consider participating and determined the number of surviving parents and siblings. If families met the inclusion criteria, study personnel requested permission to contact family members and update contact information. A summary of twin recruitment is provided in eTable 1 (http://www.archgenpsychiatry.com). Overall, recruitment was deemed reasonable given that the mean (SD) interval between interviews in cohort II and the present study is 7.2 (1.4) years. Verbal consent was obtained from each participant before starting the interview. Data collection began in 2003 and continued through 2008. Funding limitations necessitated scaling back enrollment; a decision was made to prioritize recruitment of high-risk family twins and reduce the number of targeted control families. Interviews were completed by 3434 respondents from 524 high-risk families and 373 control families. As an additional safeguard, respondents were required to provide written consent after the interview allowing use of the data obtained. Data from respondents who either returned consents requesting that their data not be used for analysis (n=17) or did not return their consents (n=10) were neither analyzed nor
