First Author:   Thor O. Thoresen Research Department, Statistics Norway, Oslo, Norway thor.olav.thoresen@ssb.no         Second Author: Peter J. Lambert Economics Dept, University of Oregon, Eugene, USA and Statistics Norway, Oslo, Norway plambert@uoregon.edu         Third Author: Runa Nesbakken Research Department, Statistics Norway, Oslo, Norway runa.nesbakken@ssb.no