Paper presented at the Final Int. Conf. of the ESF Scientific Network on Household Panel Studies held CEPS/INSTEAD Walferdasnge (LU), 1-2 Jun 1993SIGLEAvailable from British Library Document Supply Centre- DSC:9349.2264(ESF-ESNHPS-WP--77) / BLDSC - British Library Document Supply CentreGBUnited Kingdo