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T. M. McClure, I. L. Swanson, W. E. Lambert, G. A. Cioffi, S. L. Mansberger; Psychometric Properties of the Glaucoma Treatment Compliance Assessment Tool. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5459.
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We created the Glaucoma Treatment Compliance Assessment Tool (GTCAT) to determine the factors related to compliance with ocular hypotensive medications. We were interested in the construct validity and reproducibility.
We enrolled 60 consecutive glaucoma patients from a tertiary practice into this cross-sectional survey. We determined construct validity using Principal Components Analysis (PCA), internal consistency reliability, and frequency analysis of floor and ceiling effects. We used paired t-tests, Pearson’s correlations, chi-square, McNemar’s test, and Intraclass Correlation Coefficients, as applicable, to determine reproducibility.
PCA showed significant factor loadings on 8 components and 7 were consistent with the constructs of the Health Belief Model (severity, benefits, self-efficacy, barriers, knowledge, susceptibility, and cues-to-action). Of these 7 components, 4 (Severity, Benefits, Self-Efficacy and Barriers) showed acceptable internal consistency reliability (Cronbach’s α > 0.70); knowledge showed borderline reliability (α=0.64); and susceptibility had poor reliability (α = 0.38). We could not determine internal consistency for cues-to-action since it only included 1 question. We excluded 2 (8 %) out of 25 questions from the reproducibility analysis because of ceiling effects. Reproducibility was 91% (21/23). Intraclass Correlation Coefficients were excellent (r≥0.60) for 15 (75%) questions and acceptable (r≥0.40) for 18 (90%) out of 20 questions.
These preliminary data suggest that the GTCAT has good construct validity and reproducibility. Removing questions with poor reliability or ceiling effects will result in a shorter questionnaire. We need to evaluate content validity and predictive validity prior to clinical implementation.
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