Central Data Catalog

The sample was drawn using a stratified two-stage sampling design. The DREN (Direction Régionale de l'Education Nationale) are grouped to constitute strata. In the first stage, a sample of schools is selected within each stratum using probability proportional to size. In the second stage, a fixed number of students are randomly selected from each school. All selected students are sampled from the same classroom. In the case where a school has more than one classroom at the targeted grades, one classroom is randomly selected first.