Psychometrics of a new questionnaire to assess glaucoma adherence: the Glaucoma Treatment Compliance Assessment Tool (an American Ophthalmological Society thesis).
OBJECTIVE
To report the psychometrics of the Glaucoma Treatment Compliance Assessment Tool (GTCAT), a new questionnaire designed to assess adherence with glaucoma therapy.


METHODS
We developed the questionnaire according to the constructs of the Health Belief Model. We evaluated the questionnaire using data from a cross-sectional study with focus groups (n = 20) and a prospective observational case series (n=58). Principal components analysis provided assessment of construct validity. We repeated the questionnaire after 3 months for test-retest reliability. We evaluated predictive validity using an electronic dosing monitor as an objective measure of adherence.


RESULTS
Focus group participants provided 931 statements related to adherence, of which 88.7% (826/931) could be categorized into the constructs of the Health Belief Model. Perceived barriers accounted for 31% (288/931) of statements, cues-to-action 14% (131/931), susceptibility 12% (116/931), benefits 12% (115/931), severity 10% (91/931), and self-efficacy 9% (85/931). The principal components analysis explained 77% of the variance with five components representing Health Belief Model constructs. Reliability analyses showed acceptable Cronbach's alphas (>.70) for four of the seven components (severity, susceptibility, barriers [eye drop administration], and barriers [discomfort]). Predictive validity was high, with several Health Belief Model questions significantly associated (P <.05) with adherence and a correlation coefficient (R (2)) of .40. Test-retest reliability was 90%.


CONCLUSIONS
The GTCAT shows excellent repeatability, content, construct, and predictive validity for glaucoma adherence. A multisite trial is needed to determine whether the results can be generalized and whether the questionnaire accurately measures the effect of interventions to increase adherence.
Devers Eye Institute/Discoveries In Sight, Legacy Health, Portland, Oregon (Dr Mansberger, Dr Sheppler, Ms McClure, Mr VanAlstine, Ms Swanson, Ms Stoumbos), and the Department of Public Health and Preventive Medicine, Oregon Health & Science University, Portland (Dr Mansberger, Dr Lambert).
Steven L
SL
Mansberger
Christina R
CR
Sheppler
Tina M
TM
McClure
Cory L
CL
Vanalstine
Ingrid L
IL
Swanson
Zoey
Z
Stoumbos
William E
WE
Lambert
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000959:Antihypertensive Agents / Q000627:therapeutic use; D001294:Attitude to Health; D003430:Cross-Sectional Studies; D005260:Female; D017144:Focus Groups; D005901:Glaucoma / Q000188:drug therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D025341:Principal Component Analysis; D011446:Prospective Studies; D011594:Psychometrics; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D016903:Drug Monitoring
D000959:Antihypertensive Agents