title: A controlled trial of envelope colour for increasing response rates in older women.
abstract: OBJECTIVE
  Postal questionnaires are widely used in health research to provide measurable outcomes in areas such as quality of life. Participants who fail to return postal questionnaires can introduce non-response bias. Previous studies within populations over the age of 65 years have shown that response rates amongst older people can be 60% or less. The current study sought to investigate whether envelope colour affected response rates in a study about the effectiveness of screening older women for osteoporosis.
  
  
  METHODS
  A total of 2803 eligible female participants aged between 70 and 85 were sent an invitation pack from their GP practice. The invitation was either in a brown or white envelope and contained a matching pre-paid reply envelope. A study questionnaire was also sent out in brown or white envelopes 1 week after consenting to participate in the trial.
  
  
  RESULTS
  The overall response rate was 78%. There was little evidence of an effect of envelope colour on response to the invitation to participate in the trial (OR 1.04, 95% CI 0.87-1.24). Similarly, there was no influence of envelope colour on the number of participants returning their questionnaires (OR 0.99, 95% CI 0.60-1.63). There was weak evidence of an effect of envelope colour on the response rates of the consent process (OR 0.86, 95% CI 0.74-1.00). When we updated a recent meta-analysis with the results of this study, there was a non-statistically- significant trend for greater response rates with brown envelopes compared with white envelopes (OR 1.19, 95% CI 0.86-1.64, I2=92%). However, the results where influenced by one study and when this study was excluded the pooled estimate was 0.98 (95% CI 0.89-1.08, I2=0%).
  
  
  CONCLUSIONS
  This study found no evidence to suggest envelope colour has an effect on response to participate in a trial or questionnaire returns. There is weak evidence to suggest envelope colour may affect consent into a trial.
authors.affiliation: York Trials Unit, Department of Health Sciences, University of York, Heslington, York, YO10 5DD, UK. nm513@york.ac.uk
authors.forename: Natasha
authors.initials: N
authors.lastname: Mitchell
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Hewitt
authors.forename: David J
authors.initials: DJ
authors.lastname: Torgerson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D003116:Color; D003142:Communication; D015709:Correspondence as Topic; D005260:Female; D006801:Humans; D015201:Meta-Analysis as Topic; D010024:Osteoporosis; D011177:Postal Service; D011795:Surveys and Questionnaires