The effect of an internet option and single-sided printing format to increase the response rate to a population-based study: a randomized controlled trial

BACKGROUND: Paper questionnaires are a common means to collect self-reported information in population-based epidemiological studies. Over the past decades, the response rates to epidemiological studies have been decreasing which can affect the selection process of eligible subjects and lead to non-response bias. Hence, research into strategies to increase questionnaire response rates is crucial. The aim of this study was therefore to explore the effectiveness of single-sided questionnaires and an internet option for response in increasing response rates to a population-based study. METHODS: A 2×2 factorial experiment was embedded within a large population-based study of pain and pain management. Persons in the study sample were 4600 residents in Grampian (north of Scotland) aged 25 years and over who were randomly selected from health board records. Sampled persons were randomly assigned to either receive a single-sided or double-sided questionnaire with or without an internet option to respond. The study questionnaire was distributed via post. RESULTS: The overall study response rate was 36.3%. When compared to the reference group that received no intervention (response rate = 35.5%), the response rate changed only marginally when single-sided questionnaires were distributed (35.8%) or when an option to reply via the internet was provided (34.3%). A somewhat higher increase in response rates was achieved when both strategies were employed (39.6%). Overall, no significant effect on response rate was determined for each strategy or their interaction. CONCLUSIONS: Evidence from this study suggests that neither single-sided questionnaires nor the option to reply via the internet resulted in a significant increase in response rates to population-based studies.