title: Effect of reminders on mitigating participation bias in a case-control study.
abstract: BACKGROUND
  Researchers commonly employ strategies to increase participation in health studies. These include use of incentives and intensive reminders. There is, however, little evidence regarding the quantitative effect that such strategies have on study results. We present an analysis of data from a case-control study of Campylobacter enteritis in England to assess the usefulness of a two-reminder strategy for control recruitment.
  
  
  METHODS
  We compared sociodemographic characteristics of participants and non-participants, and calculated odds ratio estimates for a wide range of risk factors by mailing wave.
  
  
  RESULTS
  Non-participants were more often male, younger and from more deprived areas. Among participants, early responders were more likely to be female, older and live in less deprived areas, but despite these differences, we found little evidence of a systematic bias in the results when using data from early reponders only.
  
  
  CONCLUSIONS
  We conclude that the main benefit of using reminders in our study was the gain in statistical power from a larger sample size.
authors: Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, UK. clarence.tam@lshtm.ac.uk
authors: Clarence C
authors: CC
authors: Tam
authors: Craig D
authors: CD
authors: Higgins
authors: Laura C
authors: LC
authors: Rodrigues
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002167:Campylobacter; D002169:Campylobacter Infections / Q000453:epidemiology; D016022:Case-Control Studies; D003625:Data Collection; D003710:Demography; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D018579:Patient Selection; D011177:Postal Service; D012737:Sex Factors; D011795:Surveys and Questionnaires