1. Division of Geriatrics; University of California at San Francisco; San Francisco California
2. San Francisco Veterans Affairs Medical Center; San Francisco California
3. Institute of Social and Preventive Medicine; University of Bern; Bern Switzerland
4. Department of Biostatistics; School of Public Health; Boston University; Boston Massachusetts
5. Section of Geriatrics; School of Medicine; Boston University; Boston Massachusetts
6. Department of Epidemiology; School of Public Health; Boston University; Boston Massachusetts