Chiao et al. BMC Public Health 2012, 12:527 http://www.biomedcentral.com/1471-2458/12/527 both sexes may be due to sample selection. Our college sample remained in the protective school environment throughout the time period of this study, a factor that may contribute to a delay in engaging in premarital sex. This finding might be interpreted via the age-integrated hypothesis [38], in which an increasing strength of social bond is particularly influential to college students who remained sexually abstinent by age 20. This bond to a social institution thus serves to mitigate peer influence as well as reduce problem behaviors. This study addressed a seriously under-explored sub- ject with regard to whether stressful life events are asso- ciated with the link between adolescent cigarette/alcohol use and premarital sex [39]. As prior research suggests, individuals may engage in premarital sex to escape from stressful life events, and such an effect may last as long as 2 years [40]. Consistent with the previous study using a U.S. sample [39], our findings demonstrated experien- cing a stressful personal event was associated with a higher likelihood of engaging in premarital sex during college for both sexes in Taiwan. In addition, consider- able evidence suggests an association between stressful life events and psychological distress in adolescence. Our findings further support this relationship. Add- itional research is needed to examine the relationships between and among stressful life events, initial sexual encounters, and long-term psychological well-being. Consistent with prior research [8,33,36], family charac- teristics were found to be significantly related to later pre- marital sex among college students in Taiwan, but the results slightly differ for males versus females. The analyses suggest male college students with an educated mother were less likely to have premarital sex between 20 and 22; this relationship was not observed for female college stu- dents. In contrast, level of family income was inversely associated with increased odds of premarital sex involve- ment between 20 and 22 for female college students, but not for male college students. We suspect the differential gender effects on premarital sex may be due to the correl- ation between family SES and parenting in the college sample. While resourceful family reveals protective func- tion, lower SES background tends to perform less parental control. Additional research is thus needed to compare the family SES context between males and females, and disen- tangle the various effects including parenting. Given fam- ilies appear to be particularly influential for Taiwanese college students, understanding the ways in which family impacts sexual behavior is essential. There are two major limitations in this study. Firstly, endogeneity may be present in the relationship between substance misuse and sexual activity [41]. Hence, we adopted a cohort sample to disentangle simultaneous causation between adolescent cigarette/alcohol use and premarital sex during college. After controlling for several Page 9 of 10 other relevant variables in the model, our research was able to document the importance of substance use in pre- dicting premarital sex during college. Secondly, in a Tai- wanese context, our results may suffer from under- reporting of sexual behavior by youth due to the social de- sirability of sexual abstinence [42]. However, it should be noted extensive efforts were made in two stages to retain samples in the process. At the first stage, original samples (from Wave 1) were sent a notice of a follow-up survey. Each sample was then visited at least 3 times in order to conduct the interview at the field site. For participants who did not have access to or failed to provide consent for an interview, a second stage effort was involved. The district supervisor re-visited these samples’ family to gain access for interview. Since the survey began in 2000, New Year’s holiday greeting cards have been mailed annually to participants to maintain some contact. These efforts to generate long-term cooperative relationship with the par- ticipants since early adolescence helped to gain their trust, with less than 3% providing inconsistent answers regard- ing self-reported sexual experiences in the two surveys [8]. Conclusions In sum, our analyses clearly highlight gender differences in the temporal relationship between adolescent cigarette/alcohol use, perceived peer characteristics, stressful life and behavioral events, and the likelihood of engaging in premarital sex among Taiwanese college youth. Whereas group differences show higher propor- tions of cigarette and alcohol use among the youth who engaged in premarital sex than those who were sexually abstinent for both sexes, the multivariate analysis in the sexually abstinent group further indicates that two years later, adolescent cigarette smoking decreased as a pre- dictor of subsequent premarital sex for females, while the effect of alcohol use remained a significant predictor of premarital sex. Reducing drinking, providing immedi- ate counseling for those who experience a personal stressful event, and promoting positive attitudes toward intimate relationship before marriage during adolescents, may be helpful intervention message content in delaying the age of onset of premarital sex in young adulthood. Specifically, interventions promoting the delay of the onset of drinking and delivering appropriate sexual edu- cation during high school may be particularly useful in preventing Taiwanese college students from engaging in risky sexual behavior. Note TYP data are released to public use and can be ap- plied for research use by approval of Academia Sinica in Taiwan (http://www.typ.sinica.edu.tw).