Outcome measurement in functional somatic syndromes: SF-36 summary scores and some scales were not valid

J Clin Epidemiol. 2012 Jan;65(1):30-41. doi: 10.1016/j.jclinepi.2011.03.012. Epub 2011 Jul 20.


Objective: This study aimed to test the validity of the 36-item Short-Form Health Survey (SF-36) scales and summaries in patients with severe functional somatic syndromes (FSS), such as fibromyalgia and irritable bowel syndrome.

Study design and setting: One hundred twenty patients with severe FSS enrolled in a randomized controlled trial filled in the SF-36 questionnaire. We tested for data quality, central scaling assumptions, and agreement with the conceptual model.

Results: Most SF-36 scales were found to be valid; however, three scales (role physical, role emotional, and general health) did not satisfy predefined criteria for construct validity, internal consistency, or targeting to the sample. The correlations between SF-36 scales differed considerably from those reported in the general population. As a consequence, the SF-36 summaries, physical component summary (PCS) and mental component summary (MCS), did not accurately reflect their underlying scales and were negatively correlated (r=-0.46, 95% CI [-0.60 to -0.31]).

Conclusion: Although the SF-36 is a valuable instrument to assess perceived health in patients with severe FSS, there are problems with some of the scales and with the scoring procedure of the summaries. The SF-36 PCS may, therefore, not accurately measure the physical health status of these patients. Alternative summary measures are needed.

Publication types

  • Evaluation Study
  • Validation Study

MeSH terms

  • Adult
  • Algorithms
  • Female
  • Fibromyalgia / diagnosis
  • Health Surveys
  • Humans
  • Irritable Bowel Syndrome / diagnosis
  • Male
  • Outcome Assessment, Health Care / statistics & numerical data
  • Quality of Life
  • Randomized Controlled Trials as Topic
  • Reproducibility of Results
  • Research Design
  • Sampling Studies
  • Self-Assessment
  • Severity of Illness Index
  • Sickness Impact Profile
  • Somatoform Disorders / diagnosis*
  • Somatoform Disorders / psychology
  • Somatoform Disorders / therapy
  • Surveys and Questionnaires*
  • Syndrome