Psychometric Properties of the Reduced Version of the Glaucoma Treatment Compliance Assessment Tool (GTCAT).

PURPOSE: To measure the psychometric properties of a reduced, 27-statement version of the Glaucoma Treatment Compliance Assessment Tool (GTCAT).

METHODS: We administered the GTCAT to 183 participants who were using a single bottle of an ocular hypotensive agent, and objectively measured adherence with Medication Event Monitoring System devices over 60 days. Adherence was the number of days with correctly timed bottle openings divided by the total number of study days. Using the 47-statement GTCAT, we created a reduced GTCAT by removing statements that: (1) did not load using Principal Components Analysis (PCA); (2) did not have a univariable association with adherence; or (3) were highly correlated (.75 or higher) with another statement. We assessed the construct validity of the remaining statements using PCA and assessed the predictive validity using multiple logistic regression analysis.

RESULTS: We removed 20 statements because they did not appear in the PCA analysis; were not predictive of adherence; and/or had high correlation. PCA of the reduced GTCAT (27 statements) extracted 5 components of the Health Belief Model (knowledge, susceptibility, cues-to-action, self-efficacy, and barriers). Multiple regression showed that the 27 statements predicted adherence (Rsq = .11, p = .03).

CONCLUSIONS: The reduced version of the GTCAT is associated with adherence, which suggests that after external validation, future glaucoma medication adherence studies could use the reduced version to efficiently measure health behaviors and determine the benefit of the GTCAT to develop personalized interventions in glaucoma adherence.