Planning community-based assessments of HIV educational intervention programs in sub-Saharan Africa.

A key consideration in planning studies of community-based HIV education programs is identifying a sample size large enough to ensure a reasonable probability of detecting program effects if they exist. Sufficient sample sizes for community- or group-based designs are proportional to the correlation or similarity of individuals within communities. As a result, efficient and effective design requires reasonable a priori estimates of the correlational structure among individuals within communities. In this study, we investigate the degree of correlation among individuals within communities and regions using samples of sixth-grade adolescents from 609 local area district communities and 122 regions in 15 sub-Saharan African nations. We develop nation-specific and international summaries of these correlations using variance partitioning coefficients from multilevel models and subsequently assess the extent to which different types of background variables delineate key sources of these correlations. The results suggest persistent differences among communities and regions and that the degree of correlation among individuals within communities varied considerably by nation. The findings underscore the importance of empirically derived values of design parameters that are anchored in evidence specific to the outcome, nation and context of the planned study.