Register-based data indicated nonparticipation bias in a health study among aging people

Objectives: To examine nonparticipation in a survey by linking it with register information and identify potential nonresponse bias of inequalities in health status among aging people. Study Design and Setting: Cross-sectional questionnaire survey with clinical checkups carried out in 2002 among persons born in 1926-1930, 1936-1940, and 1946-1950 in Southern Finland. The sample was linked with register information from Statistics Finland and analyzed in terms of participation and health status as measured by medicine reimbursements. Results: Participation in the survey was more frequent among those who were older, female, married or cohabiting, higher educated and nonurban residents, and those with higher income and moderate health. Among nonrespondents, women were less healthy than men, whereas among respondents, the results were reversed. Among nonrespondents, better income was associated with unfavorable health. Poor health was generally more common among nonrespondents than respondents in several subgroups. Conclusion: Differences in response rates were found in sociodemographic factors, health, and socioeconomic position. Favorable health was generally more frequent among respondents than nonrespondents. In particular, health inequalities by gender and income differed between respondents and nonrespondents. Thus, nonresponse may lead to bias in analyses of health inequalities among aging people. (C) 2011 Elsevier Inc. All rights reserved.