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

Abstract

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.

An examination of factorial invariance of the Asthma Control Questionnaire among adults with severe asthma

“…There was some evidence of systematically differing responses to the first questionnaire item of the ACQ5 between sexes with the same degree of asthma symptom control, however average responses were considered approximately equal, consistent with the literature [15]. This is an important finding as some studies report that females have a worse perception of asthma and experience it as more symptomatic than men [44].…”

“…Strong measurement invariance of the ACQ5 was not observed when comparing patients of different ages. A study of measurement invariance of the ACQ6 among children concluded that lack of measurement invariance was due to the fifth question [15]. In our study we observed that failure to observe strong measurement invariance was due to the first question.…”

“…A small number of studies have assessed invariance of measurement instruments specific to asthma [15,16,42,43]. Measurement invariance of the ACQ6 has been assessed with regards to sex and age among children [15] and over time among adults [16]. However no such studies of the ACQ have been undertaken among severe asthmatic patients.…”

“…It is possible that our finding may reflect a general issue relating to questions assessing sleep and/or the possibility that patients with severe asthma experience different types of sleeping problems dependent on age. However, the difference in the intercept for acq1 between the oldest and youngest age-group was only 0.27 (Yan et al considered a difference of 0.19 to be small [15]).…”

“…Nevertheless, these instruments are commonly used in research settings and clinical trials among patients across the spectrum of asthma severity. To-date studies which examine the measurement properties of the ACQ in relation to asthma symptom control have been undertaken among children [15] and adults [16], however, no such studies have taken place in severe asthmatic adult populations. This patient group is important as it drives much of the morbidity and healthcare costs of asthma [17].…”