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BMJ Endgames

Questionnaire Surveys: Sources of Bias

Philip Sedgwick
Reader in medical statistics and medical education
Centre for Medical and Healthcare Education, St George’s, University of London, London, UK

Researchers investigated the attitudes of patients about the use of placebo treatments in medical care. A telephone survey was used. Participants were residents in Northern California, aged 18-75 years, who had been seen by a primary care provider for a chronic health problem at least once in the previous six months.Participants were randomly selected using age stratified sampling (10 year age groups) from all residents in Northern California who met the inclusion criteria. An introductory letter describing the study’s aims was sent to 1800 residents inviting them to participate, with the opportunity to opt out of the study. Those who did not opt out were telephoned and asked to complete the survey by phone. Sample members were excluded if they had dementia or could not participate in a telephone interview because of communication barriers (hearing, language). Of the 1800 residents sampled, 1598 were reachable by mail and potentially eligible to participate. Of these, 853 completed the telephone interview, giving a response rate of 53.4% (853/1598). 

The researchers concluded that most patients in the survey seemed favourable to the idea of placebo treatments, and that they valued honesty and transparency in this context. Respondents suggested that doctors should consider engaging with patients to discuss their values and attitudes about the appropriateness of using treatments aimed at promoting placebo responses.



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Competing interests: None declared.

  1. Hull SC, Colloca L, Avins A, Gordon NP, Somkin CP, Kaptchuk TJ, et al. Patients’ attitudes about the use of placebo treatments: telephone survey. BMJ 2013;346:f3757.
  2. Sedgwick P. Bias in clinical trials. BMJ 2011;343:d4176.

Cite this as: BMJ 2013;347:f5265

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This post is based on an article published in "Endgames" an educational series from The BMJ.  Other Endgames articles are available here. Copyright BMJ Publishing Group 2013