Sexual debut: an analysis of the birth to twenty data.
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According to the literature, it is widely accepted that the early timing of first sex among adolescents is related to long-term health effects and current and future risky sexual behaviour (Sandfort et al., 2008). Despite the importance of youth sexual behaviour for sexual and reproductive health, and the severity of the Human Immunodeficiency Virus (HIV) and the Acquired Immune Deficiency Syndrome (AIDS), there exists relatively little empirical research on sexual debut in Southern Africa (Muula, 2008). The aim of this dissertation is to utilize survival analysis techniques to determine significant predictors of early sexual debut in a South African context. A collaboration with the Human Sciences Research Council (HSRC) was fostered and access to the Birth to Twenty (Bt20) data was arranged. The data set consists of 3273 respondents who were followed from birth. Sexual exposure measures were recorded in six collection waves, namely 11-12, 13, 14, 15, 16 and 17-18 years. Multivariate analyses were initially run by employing a standard survival analysis technique, namely Cox proportional hazards regression survival analysis for sexual debut. Analyses were run separately for males and females. A log-rank test showed that there was a significant difference between the survivor curves for voluntary sexual debut and involuntary sexual debut. This result prompted consideration to explore a competing risks regression model with voluntary sexual debut as the event of interest and involuntary sexual debut as the competing risk event. SPSS was used to run exploratory analyses and Cox Regression (IBM Corp, 2012). Regression diagnostic plots were run in SAS (SAS Institute Inc, 2004). Competing risks regression was performed according to the method of Fine & Gray (1999) by evoking the STCRREG command in STATA and the validity of the proportional subhazards assumption was tested by including time interaction variables in the model (StataCorp, 2013). Where violations of the proportional subhazards assumption were found, the varyi ing effect of the hazard functions on the time to sexual debut was interpreted accordingly.