A recurrent problem in economic studies based on survey data is to determine whether survey weights should be used or not. We show that weighted estimators are more robust than unweighted ones, but less accurate when unweighted estimators are consistent. In some circumstances, a compatibility...

This document presents the different ways to model heterogeneity in case of clustering, such pupils achievement in classroom or schools. In the linear framework, it essentially discusses the pertinence of fixed or random effects assumptions depending upon the goal pursued and the empirical...