The ELSA-Brasil (Estudo Longitudinal de Saúde do Adulto -Brazilian Longitudinal Study for Adult Health) is a cohort study composed of 15,105 adults followed up in order to assess the development of chronic diseases, especially diabetes and cardiovascular disease. Its size, multicenter nature and the diversity of measurements required effective and effi cient mechanisms of quality assurance and control. The main quality assurance activities (those developed before data collection) were: careful selection of research instruments, centralized training and certifi cation, pretesting and pilot studies, and preparation of operation manuals for the procedures. Quality control activities (developed during data collection and processing) were performed more intensively at the beginning, when routines had not been established yet. The main quality control activities were: periodic observation of technicians, test-retest studies, data monitoring, network of supervisors, and cross visits. Data that estimate the reliability of the obtained information attest that the quality goals have been achieved.
2Quality assurance and control in ELSA-Brasil Schmidt MI et al Health research aims primarily to fi nd answers to diverse health issues, and the integrity of results is strongly determined by the quality of the information produced. 1,5,6 To guarantee the quality of the data in the Estudo Longitudinal de Saúde do Adulto (ELSA-Brasil -Brazilian Longitudinal Study for Adult Health), Quality Assurance and Control (QAC) tools were developed, like the ones described by Szklo & Nieto, 7 for the planning, execution and analysis of epidemiological studies.ELSA-Brasil is a cohort study that aims to follow up 15,000 participants, in six research centers, based on interviews and tests of varied complexities. These characteristics -large size, longitudinal nature, multicenter organization, measurements of distinct complexities -structured the strategic defi nition of the QAC system to be adopted.Experience in planning and conducting large longitudinal studies, especially from the 1950s onwards, has enabled the development of QAC tools to be used in cohort studies 8 and in randomized clinical trials. 4 The QAC system of Elsa-Brasil was based on this international experience, and necessary adaptations were performed by the Steering Committee and its Advisory Committees, founded on principles outlined by the QAC Committee.The present study aimed to describe the QAC actions in the ELSA-Brasil, presenting them in the sequence in which they were developed and indicating how and when key QAC decisions were adopted in the construction of the cohort and in its follow-up.
QUALITY ASSURANCEQuality assurance activities in the ELSA are defi ned by the set of actions developed before the beginning of data collection, in order to ensure the quality desired for the study's results. They are:• development of the research protocol;• selection of research instruments to fulfi ll the objectives of the study, based on literature data;• development of t...