Post-stratification to correct for nonresponse: classification of ZIP code areas

Abstract

Presently used weighting procedures for the Dutch Labor Force Survey are suspected not to correct sufficiently for bias due to nonresponse. In this paper, a new correction procedure is proposed that is based on post-stratification. Starting from small geographical units, i.e., ZIP code areas, homogeneous clusters of individuals are sought. For this purpose a two-stage strategy for cluster-analyzing the large number of ZIP code areas is presented. Because hierarchical clustering procedures cannot be applied to large numbers of objects, initial clusters of objects are sought by categorizing the cluster variables, in the first stage of the procedure. In the second stage, these initial clusters are further combined with an hierarchical procedure, resulting in a final classification. The two-stage procedure is applied to classify the ZIP code areas in the Netherlands with respect to socio-economic variables.