Background: Information on the prevalence of diseases is commonly gathered by questionnaires. Although the method is relatively inexpensive and efficient as opposed to physical examinations, the validity of the information collected is often questioned. The objective of this study was to assess the value of biometrical data complementary to self-reported questionnaire information for estimating the prevalence of hypertension and diabetes in the population at large and to examine factors that affect the accuracy of self-reporting.
Methods: Baseline data of 4950 adult participants of the Utrecht Health Project, a community-based prospective cohort study, were used to calculate sensitivity and specificity of self-reported hypertension and diabetes with the results of blood pressure measurements and blood glucose levels, corrected for current medication use, as the reference standard. Multivariate logistic regression analysis was performed to determine which participants' characteristics independently predicted the accuracy of self-reports.
Results: Overall sensitivity was 34.5% for self-reported data on hypertension and 58.9% for diabetes, while overall specificity was high for both conditions (96.4 and 99.4%, respectively). The agreement between self-reported and biometrical data was higher for diabetes than for hypertension and varied per subgroup.
Conclusions: The use of self-reported data to estimate the prevalence of hypertension and diabetes may lead to underestimated prevalence estimates and biased associations with risk factors due to differential misclassification. Adding biometrical measurements to self-reported questionnaire information will assure the validity of the data. The magnitude of the additional value of biometrical data depends on the condition studied and the characteristics of the population under investigation.