Control participants were selected from the same target population as the cases using random-digit dial and were frequency-matched to cases by sex, age within 5-year categories and county. Identification of controls older than 65 years was supplemented by random selection from the United States Health-Care Finance Administration (now the Centers for Medicare and Medicaid Services) lists. Approximately three controls were identified for each case participant. Sixty-seven percent of eligible cases and 67% of eligible controls completed an in-person interview using structured questionnaires. Written consent was obtained from each study participant prior to the interview. This study was reviewed and approved by the University of California San Francisco Committee on Human Research.
