1. Department of Epidemiology and International Health, University of California, San Francisco, San Francisco, California
2. Department of Medicine, University of California, San Francisco, San Francisco, California
3. Biostatistician, Syntex Laboratories, Palo Alto, California
4. School of Public Health, University of Minnesota, Minneapolis, Minnesota
5. Department of Behavioral and Environmental Health Sciences, School of Public Health, University of California at Berkeley, Berkeley, California