title: Implicit self-comparisons against others could bias quality of life assessments.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors: Department of Public Health, Institute of Applied Health Sciences, University of Aberdeen, Aberdeen AB24 2TN, UK. p.fayers@abdn.ac.uk
authors: Peter M
authors: PM
authors: Fayers
authors: Anne L
authors: AL
authors: Langston
authors: Clare
authors: C
authors: Robertson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001294:Attitude to Health; D015982:Bias; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D010001:Osteitis Deformans / Q000523:psychology / Q000534:rehabilitation; D011788:Quality of Life; D015203:Reproducibility of Results; D012606:Scotland; D012720:Severity of Illness Index; D016896:Treatment Outcome