Quality Control Extensive efforts will be made to ensure the quality of the data collected throughout the study. At each site, the study physicians, including review of the chart, will review the data from a randomly chosen 5 percent of screened patients and from all patients about whom the screeners had questions. Data from a random sample of 7 percent of cases were abstracted and entered into the database twice, with an error rate of less than 0.25 percent. The charts were reevaluated until the final notes, laboratory test results, and oth-er results will be completed. Complete data will be necessary to include patients in the final analysis, and we will accept patients with no missing data for the main variables or patients with missing data less than 10% for secondary variables.