Dyspnea is a primary symptom of chronic lung disease and an important outcome measure for clinical trials. Several standardized measures have been developed to evaluate this important symptom and are being used increasingly in clinical trials. The minimally clinically important difference (MCID) is not well defined for these measures but is important in interpreting the clinical meaning of results of studies in this area. The purpose of this paper is to evaluate the MCID for three commonly used measures to assess dyspnea in chronic lung disease: UCSD Shortness of Breath Questionnaire (SOBQ), Borg Scale (Borg), and Visual Analog Scale (VAS). The analysis is based on a retrospective review of published trials evaluating the response to a pulmonary rehabilitation or exercise intervention that is known to produce modest, but clinically meaningful changes for such patients. Using a distribution-based approach based primarily on effect size, the recommended MCID for these measures are: 5-units for the SOBQ, 1-unit for the Borg scale, and approximately 10 to 20 units for the VAS.
