1. Department of Sociology and Human Geography, University of Oslo, 0317 Oslo, Norway
2. Department of Sociology, Princeton University, Princeton, NJ 08544
3. National Bureau of Economic Research, Cambridge, MA 02138
4. Department of Special Needs Education, University of Oslo, 0317 Oslo, Norway
5. Department of Psychology, University of Oslo, 0317 Oslo, Norway
6. Nic Waal Institute, Lovisenberg Diaconal Hospital, 0853 Oslo, Norway
7. Department of Clinical Science, University of Bergen, 5009 Bergen, Norway