Measurement invariance of the Seattle Angina Questionnaire in coronary artery disease.

PURPOSE: The 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. This study evaluates the measurement invariance of the SAQ across different demographic and clinical groups and over time. METHODS: Data were obtained from the Alberta Provincial Project on Outcome Assessment in Coronary Heart Disease registry, a registry of patients who received coronary angiogram in Alberta, Canada. The study cohort consists of adult patients who completed the paper-based version of the 16-item Canadian version of the SAQ (SAQ-CAN) 2 weeks and 1-year post-coronary angiogram between 2009 and 2016. Multi-group confirmatory factor analysis was used to assess configural, weak, strong, and strict measurement invariance across age groups, sex, angina type, treatment, and over time. Model fit was assessed using the comparative fit index and root mean square error of approximation. RESULTS: Of the 8101 patients included in these analysis, 1300 (16.1%) were at least 75 years old, while 1755 (21.7%) were female, 5154 (63.6%) were diagnosed with acute coronary syndrome, 1177 (14.5%) received coronary artery bypass graft treatment, and 3279 had complete data on the SAQ-CAN at both occasions. There was evidence of strict invariance across age, sex, and angina type, and treatment groups, but partial strict invariance was established over time. CONCLUSION: SAQ-CAN can be used to compare the health status of coronary artery disease patients across population groups and over time.