Implicit self-comparisons against others could bias quality of life assessments

Peter Fayers, Anne Louise Langston, Clare Robertson, PRISM Trial Group

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)


Objectives: To explore how patient-reported health-related quality of life (HRQL) and global health status are affected by use of differing personal reference frames. We hypothesized that implicit comparisons against self at an earlier time, against healthy peers, or against ill patients would greatly affect patients' response values.

Study Design and Setting: Patients in a randomized trial for treatment of Paget's disease completed annual HRQL questionnaires. Supplementary questions were appended, asking the patients whether they were aware of having made implicit comparisons.

Results: The majority of patients reported considering themselves a year ago (31% at baseline), themselves before becoming ill (23%), or other healthy people (24%), with similar proportions during follow-up. Mean HRQL scores varied substantially according to the declared frame of reference, with differences as big as 19% of the scale score, or a standardized mean effect size of 0.74 standard deviations.

Conclusion: Reported reference frames were associated with effects of similar magnitude to the differences in HRQL that are regarded as clinically important. This may be of particular concern in trials that randomize patients to management in different settings, such as treatment at home/in hospital, or surgery/chemotherapy and might bias or obscure HRQL differences.

Original languageEnglish
Pages (from-to)1034-1039
Number of pages6
JournalJournal of Clinical Epidemiology
Issue number10
Early online date25 Jul 2007
Publication statusPublished - Oct 2007

Bibliographical note

We wish to acknowledge the Arthritis Research Campaign, the National Association for the Relief of Paget’s Disease, and The Alliance for Better Bone Health (Proctor & Gamble Pharmaceuticals and Sanofi Aventis) for grant support of the PRISM trial. The Health Services Research Unit is funded by the Chief Scientist Office of the Scottish Executive Department of Health. The views expressed are those of the authors and not necessarily those of the funding body. We also wish to acknowledge the support of the PRISM Trial Group.


  • quality of life
  • self-reported health
  • self-rated health
  • patient-reported outcomes
  • reference frames
  • response shift
  • rated health
  • mortality
  • care
  • oncology
  • age


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