Increasing questionnaire response: evidence from a nested RCT within a longitudinal birth cohort study
Adequate response rates are essential when using questionnaires in research, as these can affect the validity of studies and the ability to generalise the findings to a wider population. Aims: The study measured the response rate to questionnaires in a large longitudinal epidemiological study and sought to determine if any of the changes made throughout data collection had a positive impact on the response to questionnaires and readdressed any imbalance seen in response by participants level of
... deprivation. Methods: Data were taken from a prospective, comparative study, designed to examine the effects of the reintroduction of water fluoridation on children's oral health over a fiveyear period. Response rates were analysed for the first year of data collection from this sample. During this year changes were made to the questionnaire layout and cover letter to attempt to increase response rates. Additionally a nested randomised control trial compared the effect on response rates of three different participant reminders to complete questionnaires were trialled. Results: Data were available for 1824 individuals. The assessment of different reminders indicated that while sending the whole questionnaire again to non responders, resulted in the highest level of response (25%), calling participants was the only method that appeared to address the imbalance in IMD between responders (29.5, 95%CI 16.9-42.0) and non-responders (26.8, 95%CI 23.5-30.2) t(12.994) -0.446, p=0.663. Conclusions: Low response rates were recorded within this large, longitudinal study giving rise to concerns about response bias. In order to address these biases, data can be weighted in order to compensate for the skew in those taking part compared to the population. Resending the entire questionnaire again is the most effective way of reminding participants to complete the questionnaire. As this is a less labour intensive 3 method than for example, calling participants more time can then be spent targeting groups who are underrepresented in the study such as those most deprived.