Psychometrika Submission March 18, 2011 VIPSCAL Page 1 VIPSCAL: AN ALGORITHM FOR A COMBINED VECTOR IDEAL POINT MODEL K. Van Deun catholic university of leuven P.J.F. Groenen erasmus university rotterdam L. Delbeke catholic university of leuven The authors would like to thank the associate editor and three reviewers for their valuable comments and suggestions to improve the quality of this work. Requests for reprints should be sent to K. Van Deun, Department of Psychology, Catholic University of Leuven, Tiensestraat 102, B-3000 Leuven, BELGIUM. E-mail: katrijn.vandeun@psy.kuleuven.ac.be 1