Strategies to increase survey participation: A randomized controlled study in a population of breast cancer survivors

Background: Data collection by mailing questionnaires to the study population is one of the main research methods in epidemiologic studies. As participation rates are decreasing, easy-to-implement and cost-effective strategies to increase survey participation are needed. In this study, we tested the effect of a pragmatic combination of evidence-based interventions. Methods: We conducted a two-armed randomized controlled trial, nested in a cohort of breast cancer survivors (n = 1000) in the setting of a health outcomes survey. The intervention arm received a postal pre-notification, a non-monetary incentive (ballpoint with the study logo) and an alternative invitation letter in which several layout and textual adjustments were implemented according to behavioural science techniques. The alternative invitation letter also contained a QR-code through which an information video about the study could be accessed. The control arm was invited according to standard practice. Participants had the option to fill-out a questionnaire either on paper or online. A questionnaire with more than 50% of the questions answered classified as participation. Results: Overall participation rate was 62.9%. No significant difference in participation rate was observed between intervention and control arm (64.5% vs 61.3%, Risk Ratio (RR) 1.05, 95% CI [0.96 - 1.16]). Older age at study (>65 vs <51 years), and high socio-economic status (highest vs lowest quartile) were associated with higher participation rates (RR 1.30, 95% CI [1.07 - 1.57] and 1.24, 95% CI [1.09 - 1.42] respectively). In-situ carcinoma compared to invasive cancer and longer interval since treatment were associated with lower participation (RR 0.86, 95% CI [0.74 - 0.99] and RR 0.92, 95% CI [0.87 - 0.99] per 5 year increase, respectively). Conclusion: Overall, the combination of four interventions tested in this study did not improve survey participation among breast cancer survivors. The overall participation rate was relatively high, possibly due to the study population of cancer survivors.