Saris, Willem E.Gallhofer, Irmtraud N.2017-03-302017-03-302011http://hdl.handle.net/10230/28333Working paper number 23 of the series of the Research and Expertise Centre for Survey Methodology (RECSM).application/pdfengThis is an Open Access article distributed under the terms of the Creative Commons Attribution License Creative Commons Attribution 4.0 International, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properlyattributed.info:eu-repo/semantics/workingPaperinfo:eu-repo/semantics/openAccess