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