Sampling
Sampling Procedure
The sample is drawn using a three-stage stratified sampling design. The country is divided into 11 strata. Strata are defined by grouping the 17 provinces into relatively homogeneous groups, based on the average school size (number of grade 2 students) and the enrolment rate, and by separating public schools from "sous-convention" schools. Bujumbura constitutes a particular stratum as it is the only one which combines public and "sous-convention" schools.
In the first stage, a sample of schools is randomly selected in each stratum. The selection consisted of 119 schools, among which 27 were replacement schools. Replacement schools were included as some accessibility issues were foreseen.
In the second stage, a sample of classrooms is selected using simple random sampling.
In the third stage, 15 students are randomly sampled in each selected classroom.
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