In order to standardize and monitor the quality of data collection and processing, all study personnel received training and were certified for all the study procedures. Information is recorded on paper case report forms, data are entered and then checked by a second reviewer. Logical data checks are programmed and additionally performed by our systems analyst, investigators and again by our biostatisticians. For laboratory analyses, blind qualitycontrol samples are included in each biospecimen run. Telephone interviewers complete classroom training, orientation to the study population, computer modules, role play interviewing and training on study-specific protocols, and are formally evaluated at the end of training. A verbatim-recording of the interviewer and participant responses, and 10% participant re-contact allows quality-control staff to verify responses.