Using the standard error of measurement to identify important changes on the Asthma Quality of Life Questionnaire

Objectives: To establish a link between the minimal important difference (MID) and the standard error of measurement (SEM) for all responsive dimensions of the Asthma Quality of Life Questionnaire (AQLQ). Methods: Secondary data analysis of baseline and follow-up interview data from 198 outpatients with asthma enrolled in a randomized controlled trial and receiving care at a major urban academic medical center's general medicine clinics. Domain statistics for baseline and follow-up interviews were examined for the AQLQ. The baseline SEM values were compared with established AQLQ MID standards using weighted K values. Results: One SEM identified the MID in responsive AQLQ dimensions. Weighted kappa values (0.88-0.93) validated excellent agreement between these two criteria. Conclusion: This is the third study to support using one SEM to identify important individual change in health-related quality of life (HRQoL) measures. However, refinement of the process for determining a measure's clinically meaningful differences is still needed to secure a link between the SEM and the identification of relevant HRQoL change over time.