Elena M Andresen1
, Theodore K Malmstrom2
, Fredric D Wolinsky3,4
, Mario Schootman5
, J Philip Miller6
and Douglas K Miller7,8 
1
Department of Epidemiology and Biostatistics, College of Public Health and Health Professions, University of Florida Health Sciences Center, PO Box 100231 Gainesville, FL 32610, USA
2
Department of Neurology & Psychiatry, School of Medicine, Saint Louis University, 1438 South Grand Boulevard, St. Louis, MO 63104, USA
3
Iowa City Veterans Affairs Medical Center, Highway 6 West, Iowa City, Iowa 52246, USA
4
Department of Health Management and Policy, College of Public Health, University of Iowa, 200 Hawkins Drive, E205 General Hospital, Iowa City, Iowa 52242, USA
5
Departments of Medicine and Pediatrics, School of Medicine, Washington University, Campus Box 8504, 660 South Euclid Avenue, St. Louis, MO 63110, USA
6
Division of Biostatistics, School of Medicine, Washington University, Campus Box 8067, 660 South Euclid Avenue, St. Louis, MO 63110, USA
7
Indiana University Center for Aging Research, School of Medicine, Indiana University, IN, USA
8
Regenstrief Institute, Inc., 410 West 10th Street, Suite 2000, Indianapolis, IN 46202, USA