BMC Public Health 2008, 8:136 http://www.biomedcentral.com/1471-2458/8/136 the sexually active females. Consistent with our findings, using the 2003 NDHS data and focusing on never-married females, Isiugo-Abanihe and Oyediran [22] reported that 20.9% of females aged 15–19 years had ever had sexual intercourse. With regards to males, our figure (18%) is, on the whole, comparable to that of 2003 NDHS, which reported 27.4% of males aged 20–24 years as having had sex by the age of 18 years and 12.7% of males as being married by age of 20. NDHS' figure of 7.9% for the pro- portion of males that had had sex by age 15 also compares well with our figure of 9.1% for the sub-group. Based on secondary analysis of Demographic and Health Survey (DHS) data, Mensch and colleagues have reported that for West Africa the proportions of 20–24 years who had engaged in premarital sex were: 18.7% for Gabon (2000 DHS), 21.1% for Ivory Coast (1998 DHS), 22.0% for Ghana (2003 DHS), 24.7% for Benin (2001 DHS) [23]. Given the difference in age cohort and time differ- ence between the periods when the various surveys were conducted, our findings on Nigerian female sexual engagement is comparable to that of female youth in many neighboring countries but significantly lower than the rates in many Francophone countries: Cameroon (35.2%; 2004 DHS), Burkina Faso (42.5%; 2003 DHS), Chad (62.5%; 1996–97 DHS), Mali (53.5%; 2001 DHS), and Niger (74.5%; 1998 DHS). The proportion of Nige- rian adolescents engaged in sex is also lower than that found in many developed countries of Europe and North America [24,25]. The higher prevalence of females engaged in sex in our study agrees with the observation of the United States National Academies of Science that more females com- pared to males report having had sex by age 18 in sub- Saharan Africa, while in Latin America and the Caribbean it is the reverse [26]. The present finding also questions the assertion by some that females consistently underre- port and males over report their sexual activities. Likewise, an experimental study on data collection methods among unmarried adolescents in Kenya did not uncover evidence of female adolescent underreporting in face-to-face inter- views when compared with the use of audio-assisted self- interview [27]. Our finding regarding a comparatively lower tendency of females with higher levels of religiosity to initiate sex dur- ing adolescence is consistent with reports of previous studies [28,29]. As different from the findings for females, we did not find statistically significant relationship between religiosity and sexual behaviour among the males. This too is consistent with the research of Rostosky and colleagues who concluded, in their review of ten pub- lished works, that while religiosity delays the sexual debut of adolescent females, the results are mixed for adolescent males [30]. Halpern et al explored the relative impact of testosterone and religiosity on adolescent sexual behav- iour and concluded that testosterone overrode religiosity [31]. Consistent with previous reports [32], personal attitude favouring delayed sexual debut was associated with avoid- ing sexual intercourse among both males and females. The theory of planned behaviour holds that attitudes con- stitute one of the determinants of health behaviour [33]. The use of alcohol, which was not significantly associated with sexual intercourse for females, was significantly asso- ciated with sex among males in the survival analysis model with psychosocial variables. It is important to note that the proxy used in the measurement of alcohol-related practices in this study was "alcohol use in the last four weeks prior to the study", which may or may not actually reflect the use of alcohol prior to sexual debut. However, noting that association between sexual engagement and alcohol use has been reported in numerous adolescent studies in different parts of the world including in the United States [34], the Caribbean [35], and Japan [36] whereas very little focus has so far been given to such rela- tionship in the Nigerian environment, we considered it worthwhile to explore the relationship despite the poten- tial weakness of our measure. Our finding in this dimen- sion should be regarded as exploratory. The repeated observations of the association between adolescent sexual initiation and alcohol use are in agreement with Jessor's cluster of risk behaviours among adolescents [37] which, according to his problem behaviour theory [38], can be traced to a common underlying factor of unconventional- ity – the tendency to transgress social norms. Convention- ality-unconventionality has been conceptualised as a dimension underlying and summarising an orientation towards, commitment to, and involvement in the prevail- ing values, standards of behaviour, and established insti- tutions of the adult society [38]. In general, greater conventionality is associated with greater involvement in health-maintaining behaviours whereas greater uncon- ventionality relates to less involvement in health-main- taining behaviour and greater involvement in health-risky behaviours. Our findings also indicate that both males and females who have stronger belief in the efficacy of condoms and more positive attitudes to FP as well as males more con- vinced of their ability to access condoms were more likely to initiate sex during adolescence. While the association sounds logical, caution is needed since the cross-sectional nature of the study precludes deducing causality. Confi- dence that condoms will prevent unwanted pregnancy and STI can remove the "fear" element that may have inhibited a young person to engage in premarital sex. As Page 11 of 14 (page number not for citation purposes)