Peter Dalgaard1, Claus Thorn Ekstrøm2, Dorte Kronborg1. 1. Center for Statistics, Department of Finance, Copenhagen Business School, Frederiksberg, Denmark. 2. Section of Biostatistics, Department of Public Health, University of Copenhagen, Øster Farimagsgade 5 B, P.O.B. 2099, Copenhagen, 1014, Denmark. ekstrom@sund.ku.dk.