title: Incentives increased return rates but did not influence partial nonresponse or treatment outcome in a randomized trial.
abstract: OBJECTIVE
  Our aim was to analyze monetary incentives and shortening the questionnaire as means of increasing response rates in a mailed follow-up survey 1 year after inpatient psychotherapeutic treatment. Additionally, effects on partial nonresponse and the assessment of treatment outcome were examined.
  
  
  METHODS
  In a 2x2 factorial design, a sample of 3,825 patients was randomized to the two following interventions: (1) receiving a prepaid monetary incentive or none; and (2) getting a short or a long questionnaire. Treatment outcome was measured prospectively by a self-assessment instrument for psychopathology.
  
  
  RESULTS
  When using incentives, the response rate significantly increased by 7.3% (95% confidence interval [CI] 2.6-11.9%). Receiving a short questionnaire led to an augmentation of the response rate of 3.7% (95% CI 0.9-8.3%), which was not significant. The corresponding odds ratios were significantly increased for monetary incentives (1.36; 95% CI 1.30-1.88), and when abridging the questionnaire (1.15; 95% CI 1.01-1.31). However, partial nonresponse and treatment outcome were independent of the two factors.
  
  
  CONCLUSIONS
  Incentives and a shorter questionnaire led to higher return rates but did not affect partial nonresponse and self-report of treatment outcome in a randomized postal survey.
authors.affiliation: University Medical Center, Department of Medical Psychology, Martinistrasse 52, Building S35, 20246 Hamburg, Germany. dirmaier@uke.uni-hamburg.de
authors.forename: Jörg
authors.initials: J
authors.lastname: Dirmaier
authors.forename: Timo
authors.initials: T
authors.lastname: Harfst
authors.forename: Uwe
authors.initials: U
authors.lastname: Koch
authors.forename: Holger
authors.initials: H
authors.lastname: Schulz
mesh_terms: D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000628:therapy*; D008875:Middle Aged; D009042:Motivation; D010349:Patient Compliance; D017060:Patient Satisfaction; D011177:Postal Service; D011613:Psychotherapy; D012201:Reward; D017678:Sex Distribution; D011795:Surveys and Questionnaires; D016896:Treatment Outcome