ASSESSING THE MINIMAL IMPORTANT DIFFERENCE IN SYMPTOMS - A COMPARISONOF 2 TECHNIQUES

We have developed a method for estimating the minimally important diff erence (MID) for health status measures. Whereas the conventional appr oach requires patients to judge themselves relative to their memories, our method requires patients to judge themselves relative to others w ith the same condition. In this study we examined whether our method ( based on between patient differences) and the conventional method (bas ed on within-patient changes) provides comparable estimates of the MID for one health status measure: the Chronic Respiratory Questionnaire. Patients with chronic obstructive pulmonary disease who were particip ating in a supervised respiratory rehabilitation program were included if they were in stable health (n = 112). Their mean score per questio n in the Chronic Respiratory Questionnaire was 4.5 (range, 1 to 7; whe re bigger values indicate better health). Our method estimated that th e MID was 0.5 (95% confidence interval 0.4 to 0.7). This estimate was similar to the MID previously found using the conventional method. The se observations support the role of the Chronic Respiratory Questionna ire for measuring patient's symptoms, the validity of our approach for assessing the MID, and an estimate on the order of 0.5 as the thresho ld for this particular health status measure.