Measurement Invariance of the Seattle Angina Questionnaire in Coronary Artery Disease

PurposeThe Seattle Angina Questionnaire (SAQ) is a widely used patient-reported measure of health status in patients with coronary artery disease. Comparisons of SAQ scores amongst population groups and over time rely on the assumption that its factorial structure is invariant (i.e., equivalent). This study evaluates the measurement invariance of the SAQ across different demographic and clinical groups as well as over time.MethodsData were obtained from the Alberta Provincial Project on Outcome Assessment in Coronary Heart Disease registry, a population-based registry of patients who received coronary angiogram in Alberta, Canada. Health-related quality of life was measured using the 16-item Canadian version of the SAQ (SAQ-CAN). Multi-group confirmatory factor analysis was used to assess configural, weak, strong, and strict measurement invariance (MI) across age groups, sex, disease type, treatment, and over time. Model fit was assessed using the comparative fit index (CFI), and root mean square error of approximation (RMSEA).ResultsOf the 8101 patients who completed the measure at baseline, 1300 (16.1%) were at least 75 years old, while 1755 (21.7%) were female, 5154 (63.6%) were diagnosed with acute coronary syndrome, while 1177(14.5%) received coronary artery bypass graft treatment. There was evidence of strict invariance across age, sex, and disease groups, but partial strict invariance was established across treatment sub-groups and over time.ConclusionSAQ-CAN is a valid measure for comparing health-related quality of life of coronary artery disease patients across population groups and over time.