Use of factor analysis models to evaluate measurement invariance property of the Asthma Control Questionnaire (ACQ)

Purposes: To demonstrate the assessment of measurement invariance property in a health status instrument and to increase the awareness of its importance, we evaluate the measurement invariance of the Asthma Control Questionnaire (ACQ) across age and gender subgroups. Methods: Data are obtained from children 7-12 years of age at entry into a randomized trial, which evaluates the effect of a telephone coaching program on improving asthma outcome. Multi-group confirmatory factor analysis is used to assess the comparability of factor loadings and intercepts across age and gender subgroups. Since age is a continuous variable, two different categorizations (7-10 vs 11-12 and 7-9 vs 10-12) are analyzed. Results: The factor loadings and intercepts of all six items in ACQ are comparable across gender subgroups. Although the factor loadings are comparable across age 7-10 and 11-12 subgroups, one intercept is statistically but not practically different. For age 7-9 versus 10-12 subgroup comparison, the factor loadings are not comparable. Conclusion: In children, the ACQ can be used to compare asthma control construct between boys and girls and between age 7-10 and 11-12 subgroups. Measurement invariance is an important property that should be examined when the latent construct(s) are compared across different subgroups.