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Gordon Barker, Paul Cook, Malik Kahook, Jeffrey Kammer, Steven Mansberger; The Glaucoma Treatment Compliance Assessment Tool (GTCAT) has an organizational structure consistent with the Health Belief Model. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3522.
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To determine the construct validity of the Glaucoma Treatment Compliance Assessment Tool (GTCAT) towards the organizational structure of the Health Belief Model (HBM).
We used the constructs of the HBM to create the 47-item GTCAT with a 5-point Likert scale. We determined construct validity using Principal Components Analysis (PCA) with an orthogonal rotation and a > .50 cutoff for item loading into components. We used Cronbach’s alpha (α) to evaluate the internal consistency reliability of the components. GTCAT questions with floor and ceiling effects (> 90% of responses 1 or 5 on the Likert Scale) were determined using frequency analysis.
We included 184 open angle glaucoma or ocular hypertension patients on ocular hypotensive monotherapy from 3 tertiary glaucoma practices. PCA loaded 26 questions into 10 components, as determined by eigenvalues (> 1.0) and a screen plot. Six of these components were consistent with the HBM constructs of Severity, Benefits, Self-Efficacy (Medication), Self-Efficacy (Control), Barriers, and Knowledge. Another component also appeared to directly assess health behavior (Behavior). The other components were undefined as part of the HBM organizing structure. The internal consistency reliability was acceptable (α ≥ 0.70) for 6 components (Knowledge, Benefits, Self-Efficacy [Medication], Self-Efficacy [Control], Barriers, and Behavior). Severity showed borderline reliability (α = 0.67) and the remaining three undefined components showed poor reliability (α ≤ 0.30). No questions had floor or ceiling effects.
The GTCAT showed good construct validity and internal consistency, though it may be unnecessarily long. Further evaluations will assess the performance of a shorter question, and the predictive validity towards glaucoma medication adherence.
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