Abstract
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Highlights
The decrease in rates of attendance in health surveys during the last decades is a major concern
A low response rate may lead to serious selection bias
In the Oslo Health Study we have previously shown that sub-groups like young age-groups, unmarried, those not born in Norway, inner city dwellers, persons with unknown or lower secondary education, low income groups and receivers of disability benefit were underrepresented among the attendees[13]
Summary
The decrease in rates of attendance in health surveys during the last decades is a major concern. Low response rates in population studies may lead to serious selection bias. The aim of this study is to investigate the effect of sending reminders to increase the rates of attendance in the Oslo Health Study, on the distribution of demographic variables and on the prevalence estimates of selected variables. Demographic variables from public health registers were compared in persons attending directly without reminders (n=12,495), in all participants attending after up to two reminders (n=18,769) and in the total invited population (n=40,874). When comparing participants attending directly with the sample including all participants and the total invited population, the percentage in the 30 year olds increased from 20% to 22% and 28%. When comparing the sample attending directly with the sample including all participants, the prevalence of diabetes in age group 75-76 years, increased from 8 to 9% in men and from 4 to 6% in women. Increasing attendance through reminders had only minor effects on prevalence estimates and conclusions
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