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Standardizing disease-specific quality of life measures across multiple chronic conditions: development and initial evaluation of the QOL Disease Impact Scale (QDIS(R))
Open Access Articles
  • John E. Ware, Jr., University of Massachusetts Medical School
  • Barbara Gandek, University of Massachusetts Medical School
  • Rick Guyer, John Ware Research Group
  • Nina Deng, University of Massachusetts Medical School
UMMS Affiliation
Department of Quantitative Health Sciences
Publication Date
6-2-2016
Document Type
Article
Abstract

BACKGROUND: To document the development and evaluation of the Quality of life Disease Impact Scale (QDIS(R)), a measure that standardizes item content and scoring across chronic conditions and provides a summary, norm-based QOL impact score for each disease.

METHODS: A bank of 49 disease impact items was constructed from previously-used descriptions of health impact to represent ten frequently-measured quality of life (QOL) content areas and operational definitions successfully utilized in generic QOL surveys. In contrast to health in general, all items were administered with attribution to a specific disease (osteoarthritis, rheumatoid arthritis, angina, myocardial infarction, congestive heart failure, chronic kidney disease (CKD), diabetes, asthma, or COPD). Responses from 5418 adults were analyzed as five disease groups: arthritis, cardiovascular, CKD, diabetes, and respiratory. Unidimensionality, item parameter and scale-level invariance, reliability, validity and responsiveness to change during 9-month follow-up were evaluated by disease group and for all groups combined using multi-group confirmatory factor analysis (MGCFA), item response theory (IRT) and analysis of variance methods. QDIS was normed in an independent chronically ill US population sample (N = 4120).

RESULTS: MGCFA confirmed a 1-factor model, justifying a summary score estimated using equal parameters for each item across disease groups. In support of standardized IRT-based scoring, correlations were very high between disease-specific and standardized IRT item slopes (r = 0.88-0.96), thresholds (r = 0.93-0.99) and person-level scores (r > /= 0.99). Internal consistency, test-retest and person-level IRT reliability were consistently satisfactory across groups. In support of interpreting QDIS as a disease-specific measure, in comparison with generic measures, QDIS consistently discriminated markedly better across disease severity levels, correlated higher with other disease-specific measures in cross-sectional tests, and was more responsive in comparisons of groups with better, same or worse evaluations of disease-specific outcomes at the 9-month follow-up.

CONCLUSIONS: Standardization of content and scoring across diseases was shown to be justified psychometrically and enabled the first summary measure of disease-specific QOL impact normed in the chronically ill population. This disease-specific approach substantially improves discriminant validity and responsiveness over generic measures and provides a basis for better understanding the relative QOL impact of multiple chronic conditions in research and clinical practice.

Keywords
  • Disease-specific measures,
  • Health-related quality of life,
  • Item response theory,
  • Multiple chronic conditions,
  • Norm-based scoring,
  • Patient-reported outcomes,
  • Responsiveness,
  • Validity
Rights and Permissions
Copyright © Ware et al. 2016. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
DOI of Published Version
10.1186/s12955-016-0483-x
Source
Health Qual Life Outcomes. 2016 Jun 2;14:84. doi: 10.1186/s12955-016-0483-x. Link to article on publisher's site
Related Resources

Link to Article in PubMed

PubMed ID
27255462
Creative Commons License
Creative Commons Attribution 4.0
Citation Information
John E. Ware, Barbara Gandek, Rick Guyer and Nina Deng. "Standardizing disease-specific quality of life measures across multiple chronic conditions: development and initial evaluation of the QOL Disease Impact Scale (QDIS(R))" Vol. 14 (2016) ISSN: 1477-7525 (Linking)
Available at: http://works.bepress.com/john_ware/223/