Asthma Control Test and Asthma Control Questionnaire: factorial validity, reliability and correspondence in assessing status and change in asthma control

Objective: This study examined the factor structures and reliabilities of the Asthma Control Test (ACT) and the Asthma Control Questionnaire (ACQ-7; ACQ-6) and the correspondence between them in assessing both level and change in asthma control. Methods: Lung function and questionnaire data for ACT and ACQ were assessed in 113 asthma patients at the beginning (T1) and the end (T2) of inpatient rehabilitation. Confirmatory factor analyses, composite reliability coefficients, Pearson correlations, Cohen's Kappa and positive/negative agreements were computed. Results: Unidimensional factor structure was confirmed for ACT. For ACQ configural invariance (i.e. same factor structure) over time could not be established. Furthermore, in ACQ-7, FEV1 showed no relation to the latent factor. Reliability estimates were 0.86-0.88 (ACT), 0.88-0.92(ACQ-6) and 0.81-0.86 (ACQ-7). Pearson correlations between ACT and ACQ were between 0.75 and 0.90 and tended to be higher at T2. If the aim is to identify patients with either not well-controlled asthma or change in asthma control, concordance was at least moderate (Kappa=0.52-0.72). Correspondence tended to be lower in identifying patients with well-controlled asthma (Kappa=0.30-0.79). In some circumstances, ACQ-6 showed higher agreement with ACT than did ACQ-7. Conclusions: ACT is a unidimensional measure, but factor structure of ACQ remains unclear. Correspondence between ACT and ACQ depends on the aim of the assessment. Including FEV1 in the assessment of asthma control level even lowers reliability of ACQ and concordance with ACT. Our results support GINA (2014) in conceptualizing FEV1 as a risk factor for poor asthma outcome instead of an indicator of level of asthma control.