title: Improving response rates using a monetary incentive for patient completion of questionnaires: an observational study.
abstract: 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.
authors.affiliation: Department of Health Sciences, York Trials Unit, Seebohm Rowntree Building, University of York, Heslington, York YO10 5DD, UK. sb143@york.ac.uk
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Brealey
authors.forename: Christine
authors.initials: C
authors.lastname: Atwell
authors.forename: Stirling
authors.initials: S
authors.lastname: Bryan
authors.forename: Simon
authors.initials: S
authors.lastname: Coulton
authors.forename: Helen
authors.initials: H
authors.lastname: Cox
authors.forename: Ben
authors.initials: B
authors.lastname: Cross
authors.forename: Fiona
authors.initials: F
authors.lastname: Fylan
authors.forename: Andrew
authors.initials: A
authors.lastname: Garratt
authors.forename: Fiona J
authors.initials: FJ
authors.lastname: Gilbert
authors.forename: Maureen G C
authors.initials: MG
authors.lastname: Gillan
authors.forename: Maggie
authors.initials: M
authors.lastname: Hendry
authors.forename: Kerenza
authors.initials: K
authors.lastname: Hood
authors.forename: Helen
authors.initials: H
authors.lastname: Houston
authors.forename: David
authors.initials: D
authors.lastname: King
authors.forename: Veronica
authors.initials: V
authors.lastname: Morton
authors.forename: Jo
authors.initials: J
authors.lastname: Orchard
authors.forename: Michael
authors.initials: M
authors.lastname: Robling
authors.forename: Ian T
authors.initials: IT
authors.lastname: Russell
authors.forename: David
authors.initials: D
authors.lastname: Torgerson
authors.forename: Valerie
authors.initials: V
authors.lastname: Wadsworth
authors.forename: Clare
authors.initials: C
authors.lastname: Wilkinson
mesh_terms: 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