Abstract
BackgroundMost health surveys have experienced a decline in response rates. A structured approach to evaluate whether a decreasing - and potentially more selective - response over time biased estimated trends in health behaviours is lacking. We developed a framework to explore the role of differential non-response over time. This framework was applied to a repeated cross-sectional survey in which the response rate gradually declined.MethodsWe used data from a survey conducted biannually between 1995 and 2017 in the city of Rotterdam, The Netherlands. Information on the sociodemographic determinants of age, sex, and ethnicity was available for respondents and non-respondents. The main outcome measures of prevalence of sport participation and watching TV were only available for respondents. The framework consisted of four steps: 1) investigating the sociodemographic determinants of responding to the survey and the difference in response over time between sociodemographic groups; 2) estimating variation in health behaviour over time; 3) comparing weighted and unweighted prevalence estimates of health behaviour over time; and 4) comparing associations between sociodemographic determinants and health behaviour over time.ResultsThe overall response rate per survey declined from 47% in 1995 to 15% in 2017. The probability of responding was higher among older people, females, and those with a Western background. The response rate declined in all subgroups, and a faster decline was observed among younger persons and those with a non-Western ethnicity as compared to older persons and those with a Western ethnicity. Variation in health behaviours remained constant. Prevalence estimates and associations did not follow the changes in response over time. On the contrary, the difference in probability of participating in sport gradually decreased between males and females, while no differential change in the response rate was observed.ConclusionsProviding insights on non-response patterns over time is essential to understand whether declines in response rates may have influenced estimated trends in health behaviours. The framework outlined in this study can be used for this purpose. In our example, in spite of a major decline in response rate, there was no evidence that the risk of non-response bias increased over time.
Highlights
Most health surveys have experienced a decline in response rates
The overall response rate declined from 47% in 1995 to 15% in 2017
We provided a framework to assess whether non-response patterns over time resulted in biased trends in health behaviours
Summary
Most health surveys have experienced a decline in response rates. A structured approach to evaluate whether a decreasing - and potentially more selective - response over time biased estimated trends in health behaviours is lacking. Most surveys have experienced major decreases in response rates over the past decades [1,2,3] This increases the possibility of selective participation that may bias estimates of prevalence of health behaviours and associations between determinants and health behaviours. Correcting for the selective participation for outcomes is often not possible given that, in most surveys, the outcome among those who do not respond is unknown To make it more complex, the combination of both mechanisms of selective participation may occur, whereby unhealthy younger persons respond less than healthy older persons, resulting in a gross underestimation of the prevalence of disease and overestimation of health behaviour
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