Use of medications by elderly Brazilian retirees: 1--methodology and response rates of a multicenter survey

This paper reports methodological aspects and response rates of a survey with the main objective of describing the drug utilization profile of retirees of the Institute of National Social Security of Brazil, 60 years of age or older, in three simple random samples: Brazil (countrywide), Belo Horizonte municipality, and Rio de Janeiro municipality. This cross-sectional study employed two approaches: mail (self-report questionnaires) and home interviews (questionnaires completed by interviewers). This strategy allowed evaluation of response agreement between the mail and home interview approaches. In the national sample of 3,000 individuals, 1,025 only responded to the self-report questionnaire. Despite this the low response rate, there was reasonable resemblance between respondents and non-respondents, suggesting that this sample is representative of the target population. In Belo Horizonte and Rio de Janeiro the initial samples of 800 individuals were replicated for both approaches, mail and home interview. The response rates to the mail surveys were 46.8% and 34.4% in Belo Horizonte and Rio de Janeiro, respectively. The response rates to the home interviews were 80.3% and 70.7% in Belo Horizonte and Rio de Janeiro, respectively, after unavoidable attrition.