We recruited participants from an entering freshman class at a large public Southwestern university beginning in 2004. A subset of those invited to participate (N = 6,391) indicted potential interest and met inclusion criteria of being first-time students between the ages of 17 and 19 years old, unmarried, and providing valid contact information (N = 4,832, 75.6%). A group of eligible participants (N = 3,046) were randomized to complete a series of repeated surveys, with the first given during the summer after the end of high school and the remaining surveys given over six years. The final sample included in the externalizing factor model analysis comprises those who provided informed consent and completed the first longitudinal survey (N = 2,245). A majority of respondents in the full survey sample were female (N = 1,345, 59.9%). The flow of participants from initial invitation and recruitment in 2004 to the provision of saliva samples and the most recent survey data in summer 2014 is presented in Supplemental Figure S1.
