BMC Public Health 2008, 8:136 http://www.biomedcentral.com/1471-2458/8/136 the Extended Parallel Process Model [39] hypothesises and empirical studies have shown [40], the element of fear plays an important role in the decision-making about sex. Likewise, an adolescent's conviction of his ability to get condom when he needs it, particularly when con- vinced of its efficacy, may have a disinhibiting effect on sexual behaviour. On the other hand, it is equally possible that sexual debut precedes the condom-related attitude we measured. Sexually active adolescents may have sought more information on the sources for and effectiveness of condoms and through first-hand experience prove its effi- cacy and their ability to access condom. Studies have shown that improved access to condoms can lead to more condom acquisition by high-school adolescents though may not necessarily lead to increases in either sexual activ- ity or condom use [41]. When looking at the relationships between attitudes toward gender equity and sexual debut in adolescence we found that Nigerian female adolescents who reported more positive attitudes toward gender equality and less tolerance of gender-based violence were also more likely than peers to report having had premarital sex. Perhaps these findings are also consistent with Jessor's unconven- tionality hypothesis on the clustering of risk behaviours. Maybe it reflects a more liberal attitude which is also reflected in more openness to sexual initiation. Further research is needed to answer this question. The present analyses showed significant regional differ- ence in the proportion of sexually active males (12.1% north, 24.3% south; X2= 29.289, p < 0.001) and females (13.1% north, 28.7% south; X2= 30.286, p < 0.001) at bivariate level as well at multivariate level when only selected socio-demographic factors were included in the model (males: HR = 1.44, 95% CI = 1.07–1.9; females HR = 51.7; 95% CI = 11.22–2.40). However, region was not a significant independent factor when psychosocial and other factors were added to the model. Thus, it is likely but uncertain that factors other than geography distinguished the more conservative and largely Islamic North from the South with her more educated, more urban and largely Christian population. The difference recorded between the North and the South in the present study does not reflect per se actual differences in proportion of sexually active adolescents; rather, the differences are among those who initiate intercourse in premarital context. As the NDHS shows, the practice of adolescent marriage is far more prevalent in the North compared to the South [3]. Thus, a major difference between the regions regarding adolescent sexual engagement is the context of sexual activity: mostly intra-marital in the North and predomi- nantly pre-marital in the South. Among sexually experienced adolescents, our comparison of early and later sexual debutants surprisingly identified only few statistically significant factors at bivariate level. Literacy in English language and alcohol use were signifi- cant factors among males while some levels of education, religiosity and media exposure were significant factors among females. The reasons for this finding are not clear, but one possibility is that the power of the study to detect the differences between the two groups is low. The issue deserves further study. One of the challenges to studying sexual behaviour is the question of the validity of the data due to recall and social desirability biases. By focusing on age 15–19 years, the possibility of recall bias, which has been noted to increase with age [42], is limited in our study. Limiting the analysis to the 15–19 age group also makes the picture more cur- rent in terms of associating timing of sexual debut and potential predictive factors. Our use of survival analysis made for adequate allowance for age censoring and avoids a common error in studies of age at first sex among adolescents [43]. A major limitation of our study, however, is that it is cross- sectional, which necessarily limits causal conclusions. In addition, some of the psychosocial factors may not have actually preceded sexual initiation. To address the limita- tion relating to the uncertainty of the temporal relation- ship between the independent variables, particularly the psychosocial factors, and sexual initiation, we presented two different survival analysis models. Whereas one excluded the psychosocial and other factors that may have uncertain temporal relationship, the other incorporated all the factors of interest in the study. With the difference in the factors identified between the two models, there is a need for further study about antecedents and predictors of adolescent sexual initiation among Nigerian adoles- cents using longitudinal approach. Our interest in this study is the never-married adolescents, and we recognise that this category may be substantially different from that of the married adolescent with regards to several contextual as well as sexual behavioural factors. Early marrying adolescents may, for example, be more likely to have an early premarital sexual debut and lesser education and, thus, their exclusion poses a challenge in terms of external validity of the results. The result of our study may not be generalised to all adolescents in Nigeria particularly with the fairly high rate of marriage among adolescent females and the associated geographic diver- sity within the national context. Nevertheless, our findings have significant implications for adolescent sexual and reproductive interventions in Nigeria since abstinence still constitutes a primary pillar Page 12 of 14 (page number not for citation purposes)