This data was part of a larger study. Sample selection
in the larger study was conveniently chosen at junior
and senior schools within 60 km of Gaborone, Botswana.
More schools in the region were sampled by
selecting a stratified random sample and choosing
only 2 classes at each school with an estimated class
size of 40. This yielded 4 junior schools and 5 senior
schools and the only university in the country