1. Center for Economic and Social Research, University of Southern California , Los Angeles, California , USA
2. Institute for Gerontology, College of Health and Welfare, Jönköping University , Jönköping , Sweden
3. Department of Psychiatry, University of California, San Diego , San Diego, California , USA
4. Center for Behavior Genetics of Aging, University of California, San Diego , San Diego, California , USA
5. Centre for Healthy Brain Ageing (CHeBA), Discipline of Psychiatry and Mental Health, School of Clinical Medicine, UNSW , Sydney , Australia
6. Danish Aging Research Center, Department of Public Health, University of Southern Denmark , Odense , Denmark
7. The Danish Twin Registry, University of Southern Denmark , Odense , Denmark
8. Departments of Psychiatry and Neurology, Duke University School of Medicine , Durham, North Carolina , USA
9. Department of Psychology and Brain and Health, University of Nevada, Las Vegas , Las Vegas, Nevada , USA
10. Department of Medical Epidemiology and Biostatistics, Karolinska Institutet , Stockholm , Sweden