Unconditional and conditional monetary incentives to increase response to mailed questionnaires: A randomized controlled study within a trial (SWAT)

Young, Ben; Bedford, Laura; das Nair, Roshan; Gallant, Stephanie; Littleford, Roberta; Robertson, John F.R.; Schembri, Stuart; Sullivan, Frank M.; Vedhara, Kavita; Kendrick, Denise; ECLS Study Team

Abstract

Rationale, aims, and objectives: High response rates to research questionnaires can help to ensure results are more representative of the population studied and provide increased statistical power, on which the study may have been predicated. Improving speed and quality of response can reduce costs.

Method: We conducted a randomised Study Within A Trial (SWAT) to assess questionnaire response rates, reminders sent and data completeness with unconditional compared to conditional monetary incentives. Eligible individuals were mailed a series of psychological questionnaires as a follow-up to a baseline host trial questionnaire. Half received a £5 gift voucher with questionnaires (unconditional) and half were promised the voucher after returning questionnaires (conditional).

Results: Of 1079 individuals, response rates to the first follow-up questionnaire were 94.2% and
91.7% in the unconditional and conditional monetary incentive groups respectively (OR 1.78, 95% CI
0.85 to 3.72). There were significantly greater odds of returning repeat questionnaires in the unconditional group at six months (OR 2.97, 95% CI 1.01 to 8.71; p = 0.047) but not at 12 months
(OR 1.12, 95% CI 0.44 to 2.85). Incentive condition had no impact at any time point on the proportion of sent questionnaires that needed reminders. Odds of incomplete questionnaires were significantly greater at three months in the unconditional compared to the conditional incentive group (OR 2.45, 95% CI 1.32 to 4.55; p = 0.004).

Conclusions: Unconditional monetary incentives can produce a transitory greater likelihood of mailed questionnaire response in a clinical trial participant group, consistent with the direction of effect in other settings. However, this could have been a chance finding. The use of multiple strategies to promote response may have created a ceiling effect. This strategy has potential to reduce administrative and postage costs, weighed against the cost of incentives used, but could risk compromising the completeness of data.

Citation

Young, B., Bedford, L., das Nair, R., Gallant, S., Littleford, R., Robertson, J. F., …ECLS Study Team. (2020). Unconditional and conditional monetary incentives to increase response to mailed questionnaires: A randomized controlled study within a trial (SWAT). Journal of Evaluation in Clinical Practice, 26(3), 893-902. https://doi.org/10.1111/jep.13230

• Journal Article Type: Article
• Acceptance Date: Jun 16, 2019
• Online Publication Date: Jul 22, 2019
• Publication Date: 2020-06
• Deposit Date: Jun 18, 2019
• Publicly Available Date: Jul 23, 2020
• Journal: Journal of Evaluation in Clinical Practice
• Print ISSN: 1356-1294
• Electronic ISSN: 1365-2753
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 26
• Issue: 3
• Pages: 893-902
• DOI: https://doi.org/10.1111/jep.13230
• Keywords: Public Health, Environmental and Occupational Health; Health Policy
• Public URL: https://nottingham-repository.worktribe.com/output/2204208
• Publisher URL: https://onlinelibrary.wiley.com/doi/abs/10.1111/jep.13230
• Additional Information: This is the peer reviewed version of the following article: Young, B, Bedford, L, das Nair, R, et al. Unconditional and conditional monetary incentives to increase response to mailed questionnaires: A randomized controlled study within a trial (SWAT). J Eval Clin Pract. 2019; 1– 10. , which has been published in final form at https://doi.org/10.1111/jep.13230. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.