We performed a multivariate survival analysis by using the Cox proportional hazards regression procedure program from the SPSS software package version 13 (SPSS Inc., Chicago, IL). This procedure allows for both time-independent and time-dependent predictors (independent variables). The event of interest was onset of sexual intercourse and the time variable was age at first consensual intercourse if less than or equal to 16 years old. Those not yet sexually active at age 16 or younger were considered to be censored and the time variable was 16. In a survival analysis, the participant's survival time is taken into account even if the individual does not yet experience the event(s) of interest. We selected age 16 as a cutoff for sexual debut since past research has classified sexual debut at age 17 or older as “late initiation” (Rosenthal et al., 2001).
