Tarozzi (2007) argues that such reweighting produces comparable outcome distributions. Depvar= 1 is defined as being in a sample of interest, or “target” sample, which, in this case, means the sample of PISA students in 2000. Depvar equals 0 for students sampled in 2003 or 2006, depending on a comparison made. Conditional probabilities are estimated using logit regression with a set of student and family characteristics defined in the same way in all waves of the PISA survey, and recoded to have similar categories.