Sample size
sexual behaviors
The overall sample size was calculated based on the number of adolescents required to derive differences, if any, in knowledge and behavioural variables that meet the criteria in each school and each selected grade, and thus more applicable in later analysis, while noting adequacy for lower-level variables, such as pregnancies. Thus, according to the Ministry of Education Statistical Bulletin of 2014, the estimated average number of students per classroom in North-Western Province is 55 for grades 1–7 and 45 for grades 8–12, with an average of two classroom streams per grade. Accounting for a 10% refusal rate, the minimum sample at each cross-sectional assessment was, therefore, 1704 adolescents, with upward adjustments to avoid in-classroom student discrimination, and maintaining enough power to test levels of significant differences in reported knowledge and sexual behaviors, irrespective of attrition due to in-school pregnancies.Z = Z value (e.g., 1.96 for 95% confidence level)p = percentage picking a choice, expressed as decimal (.5 used for sample size needed)c = confidence interval, expressed as decimal.