Discovering the Dynamics of the Minimal Clinically Important Difference of Health Status Instruments in Patients with Chronic Obstructive Pulmonary Disease

The change score on a test or questionnaire that represents an important improvement or deterioration for a patient, is referred to as the minimal clinically important difference (MCID). MCIDs are a mandatory lower limit for the approval and evaluation of new treatments. It is therefore very important that correct MCIDs are determined. In this thesis, the MCIDs of several questionnaires were calculated, compared with each other and investigated for factors influencing this measurement. The study was conducted in people with chronic obstructive pulmonary disease (COPD) with the three main health status questionnaires. Data were collected from (1) a literature review; (2) a clinical study in a German pulmonary rehabilitation clinic; and (3) a questionnaire study in Dutch COPD patients treated by their general practitioner and/or pulmonary physician.Small differences were observed for the questionnaire MCIDs between multiple approaches used and during various follow-up periods. Despite minor differences, the MCIDs for people with an improved health status were found to be fairly similar to those for people with an experienced deterioration. Furthermore, the MCIDs for patients in the German pulmonary rehabilitation study were higher than for Dutch routine care patients. Moreover, a larger relevant improvement in health status (a higher MCID) was noted for patients, who already had many symptoms and limitations at the start of the study. This was similar for women, participants aged 60 years or over, patients with a good lung function, and people with fewer co-morbid diseases. However, these patient groups needed only little additional deterioration in health status (a lower MCID) to actually feel worse.