Background: The Finbalt Health Monitor is a collaborative system for monitoring the health-related behaviour, practices and lifestyles in Estonia, Finland, Latvia and Lithuania. This system is based on nationally representative samples and self-administered mailed questionnaires. In comparing the results of national surveys, the awareness of the direction and socioeconomic patterning of the response bias is essential.
Methods: The data were gathered from the cross-sectional surveys conducted in 1998 from Estonia (n = 1362), Finland (n = 3504), Latvia (n = 2322) and Lithuania (n = 1874). An analysis was made of the prevalence of late response, completeness of information obtained from respondents and the magnitude of response bias on the prevalence estimates of health behaviour indicators.
Results: The response rates were comparatively high: 68% in Estonia, 70% in Finland, 77% in Latvia and 62% in Lithuania. Late response was weakly related to age, education or place of residence. The total proportion of missing information was below 10% and the sociodemographic patterning for this missing information was similar in all countries. Thus, older and less-educated respondents had more missing information on their questionnaires. Response bias of the prevalence estimates was minimal when it was calculated by using information obtained from late respondents.
Conclusions: The level of nonresponse and missing information was comparable in different countries, not information on health behaviour. Therefore special efforts are needed to design a questionnaire form which appears equally relevant to all respondent groups. The follow-up mailings were an effective way to increase the total response rate, but it was unlikely that they provided an effective way to reach the 'hard core' nonrespondents.