Improving response rates using a monetary incentive for patient completion of questionnaires: an observational study.
BACKGROUND
Poor response rates to postal questionnaires can introduce bias and reduce the statistical power of a study. To improve response rates in our trial in primary care we tested the effect of introducing an unconditional direct payment of 5 pounds for the completion of postal questionnaires.


METHODS
We recruited patients in general practice with knee problems from sites across the United Kingdom. An evidence-based strategy was used to follow-up patients at twelve months with postal questionnaires. This included an unconditional direct payment of 5 pounds to patients for the completion and return of questionnaires. The first 105 patients did not receive the 5 pounds incentive, but the subsequent 442 patients did. We used logistic regression to analyse the effect of introducing a monetary incentive to increase the response to postal questionnaires.


RESULTS
The response rate following reminders for the historical controls was 78.1% (82 of 105) compared with 88.0% (389 of 442) for those patients who received the 5 pounds payment (diff = 9.9%, 95% CI 2.3% to 19.1%). Direct payments significantly increased the odds of response (adjusted odds ratio = 2.2, 95% CI 1.2 to 4.0, P = 0.009) with only 12 of 442 patients declining the payment. The incentive did not save costs to the trial--the extra cost per additional respondent was almost 50 pounds.


CONCLUSIONS
The direct payment of 5 pounds significantly increased the completion of postal questionnaires at negligible increase in cost for an adequately powered study.
Brealey
Stephen D
SD
Department of Health Sciences, York Trials Unit, Seebohm Rowntree Building, University of York, Heslington, York YO10 5DD, UK. sb143@york.ac.uk
Atwell
Christine
C
Bryan
Stirling
S
Coulton
Simon
S
Cox
Helen
H
Cross
Ben
B
Fylan
Fiona
F
Garratt
Andrew
A
Gilbert
Fiona J
FJ
Gillan
Maureen G C
MG
Hendry
Maggie
M
Hood
Kerenza
K
Houston
Helen
H
King
David
D
Morton
Veronica
V
Orchard
Jo
J
Robling
Michael
M
Russell
Ian T
IT
Torgerson
David
D
Wadsworth
Valerie
V
Wilkinson
Clare
C
D005249:Fees and Charges; D006801:Humans; D007592:Joint Diseases / Q000601:surgery / Q000628:therapy*; D007719:Knee Joint; D008279:Magnetic Resonance Imaging; D019637:Orthopedic Procedures; D018579:Patient Selection; D010361:Patients; D011795:Surveys and Questionnaires / Q000191:economics*; D006113:United Kingdom