title: The Validity of Disease-specific Quality of Life Attributions Among Adults with Multiple Chronic Conditions.
abstract: BACKGROUND
  A crucial assumption underlying all disease-specific quality of life (QOL) measures, that patients can validly differentiate a specific diseasein the presence of multiple chronic conditions, has not been tested using multiple methods. Our objective was to evaluate the convergent and discriminant validity of QOL attributions to specific diseases among adults with multiple chronic conditions (MCC).
  
  
  METHODS
  Adults age 18 and older (N=4,480) sampled from eight pre-identified condition groups (asthma, COPD, angina/MI with angina, congestive heart failure, diabetes, chronic kidney disease, osteoarthritis, rheumatoid arthritis) completed an Internet survey. Comorbid conditions were determined using a 35-condition checklist. Product-moment correlations were analyzed separately by pre-identified condition group using the multitrait-multimethod of construct validation, where traits were defined by 9-26 conditions and each condition was measured by two methods: disease severity rating and Disease-specific Quality of Life Impact Scale (QDIS) global rating. A third method (symptom or clinical marker) was available for the eight pre-identified conditions.Convergent validitywas supported when correlations amongdifferent methods of measuring the same condition(trait) were substantial (r≥0.40).Discriminant validitywas supported when correlations between thesame and different methods of measuring different conditionswere significantly lower than corresponding convergent correlations.
  
  
  RESULTS
  In support of convergent validity, 22 of 24 convergent correlations were substantial (r=0.38-0.84, median=0.53). In support of discriminant validity, 833 of 924 tests (90.2%) yielded significantly higher convergent than discriminant correlations across the eight pre-identified conditions. Exceptions to this pattern of results were most often observed for comorbid conditions within the same clinical area.
  
  
  CONCLUSIONS
  Collectively, convergent and discriminant test results support the construct validity of disease-specific QOL impact attributions across MCC within the eight pre-identified conditions. Noteworthy exceptions should be considered when interpreting some specific QOL impact attributions and warrant further study. Pursuit of a summary disease-specific QOL impact score standardized across MCC is recommended.
authors.affiliation: University of Massachusetts Medical School, Worcester, MA; John Ware Research Group, Watertown, MA.
authors.forename: John E
authors.initials: JE
authors.lastname: Ware
authors.affiliation: University of Massachusetts Medical School, Worcester, MA; John Ware Research Group, Watertown, MA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Gandek
authors.affiliation: University of Massachusetts Medical School, Worcester, MA.
authors.forename: Jeroan
authors.initials: J
authors.lastname: Allison
keywords: Disease-specific measures; Health-related quality of life; Multiple chronic conditions; Multitrait-multimethod analysis; Patient-reported outcomes; Validity