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

Abstract

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). 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 kappa values. One SEM identified the MID in responsive AQLQ dimensions. Weighted kappa values (0.88-0.93) validated excellent agreement between these two criteria. 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.