title: Dependence of the minimal clinically important improvement on the baseline value is a consequence of floor and ceiling effects and not different expectations by patients.
abstract: OBJECTIVE
  Estimates of minimal clinically important improvements (MCIIs) are larger among patients with higher values at baseline, suggesting that these patients require larger changes to appreciate improvements. We examined if baseline dependency of MCIIs was associated with specific patients across three measures, or was owing to floor and ceiling effects.
  
  
  METHODS
  We prospectively examined 250 outpatients with active rheumatoid arthritis (RA). We used an anchor-based approach to estimate MCIIs for three measures of RA activity (patient global assessment, swollen joint count, and walking time). We examined if the same patients constituted the baseline subgroups with high MCIIs across measures.
  
  
  RESULTS
  The MCIIs were greater for those with higher baseline values of all three measures. At the ceiling, there was little opportunity to improve, and judgments were unrelated to measured changes. At midrange, improvements were balanced by worsenings, including some judged as improvements. At the floor, improvements were not similarly balanced. Patients in subgroups with high MCII for patient global assessment were not also predominantly in subgroups with high MCII for the swollen joint count or walking time, and vice versa.
  
  
  CONCLUSIONS
  Variation in MCII by baseline values is because of floor and ceiling effects rather than expectations of particular patients.
authors.affiliation: Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address: wardm1@mail.nih.gov.
authors.forename: Michael M
authors.initials: MM
authors.lastname: Ward
authors.affiliation: Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Lori C
authors.initials: LC
authors.lastname: Guthrie
authors.affiliation: Intramural Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Alba
mesh_terms: D000328:Adult; D000553:Ambulatory Care; D001172:Arthritis, Rheumatoid / Q000503:physiopathology* / Q000628:therapy*; D001294:Attitude to Health; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010361:Patients / Q000523:psychology* / Q000706:statistics & numerical data; D011446:Prospective Studies; D012720:Severity of Illness Index; D016896:Treatment Outcome
keywords: Ceiling effect; Floor effect; Minimal clinically important difference; Outcome measures; Responsiveness; Rheumatoid arthritis