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Does a monetary incentive improve the response to a postal questionnaire in a randomised controlled trial? : the MINT incentive study

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Gates, Simon, Williams, Mark A., Withers, Emma J., Williamson, Esther M., Mt-Isa, Shahrul and Lamb, S. E. (Sallie E.). (2009) Does a monetary incentive improve the response to a postal questionnaire in a randomised controlled trial? : the MINT incentive study. Trials, Vol.10 . p. 44. ISSN 1745-6215

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Official URL: http://dx.doi.org/10.1186/1745-6215-10-44

Abstract

Background: Sending a monetary incentive with postal questionnaires has been found to improve
the proportion of responders, in research in non-healthcare settings. However, there is little
research on use of incentives to improve follow-up rates in clinical trials, and existing studies are
inconclusive. We conducted a randomised trial among participants in the Managing Injuries of the
Neck Trial (MINT) to investigate the effects on the proportion of questionnaires returned and
overall non-response of sending a £5 gift voucher with a follow-up questionnaire.
Methods: Participants in MINT were randomised to receive either: (a) a £5 gift voucher (incentive
group) or (b) no gift voucher (no incentive group), with their 4 month or 8 month follow-up
questionnaire. We recorded, for each group, the number of questionnaires returned, the number
returned without any chasing from the study office, the overall number of non-responders (after
all chasing efforts by the study office), and the costs of following up each group.
Results: 2144 participants were randomised, 1070 to the incentive group and 1074 to the no
incentive group. The proportion of questionnaires returned (RR 1.10 (95% CI 1.05, 1.16)) and the
proportion returned without chasing (RR 1.14 (95% CI 1.05, 1.24) were higher in the incentive
group, and the overall non-response rate was lower (RR 0.68 (95% CI 0.53, 0.87)). Adjustment for
injury severity and hospital of recruitment to MINT made no difference to these results, and there
were no differences in results between the 4-month and 8-month follow up questionnaires.
Analysis of costs suggested a cost of £67.29 per additional questionnaire returned.
Conclusion: Monetary incentives may be an effective way to increase the proportion of postal
questionnaires returned and minimise loss to follow-up in clinical trials.

Item Type:	Journal Article
Subjects:	R Medicine > R Medicine (General) H Social Sciences > HA Statistics
Divisions:	Faculty of Medicine > Warwick Medical School > Health Sciences Faculty of Medicine > Warwick Medical School
Library of Congress Subject Headings (LCSH):	Medical care surveys -- Response rate, Mail surveys -- Response rate, Nonresponse (Statistics), Incentive (Psychology), Clinical medicine -- Research
Journal or Publication Title:	Trials
Publisher:	BioMed Central Ltd.
ISSN:	1745-6215
Official Date:	22 June 2009
Volume:	Vol.10
Number of Pages:	7
Page Range:	p. 44
Identification Number:	10.1186/1745-6215-10-44
Status:	Peer Reviewed
Access rights to Published version:	Open Access
Funder:	NHS R & D HTA Programme (Great Britain) (HTA)
Grant number:	02/35/02 (HTA)
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URI:	http://wrap.warwick.ac.uk/id/eprint/2261