Small, Moderate, and Large Changes, and the Minimum Clinically Important Difference in the University of California, San Diego Shortness of Breath Questionnaire

Minimum clinically important change of 5 points in the University of California, San Diego Shortness of Breath Questionnaire (SOBQ) is established, but cutoff values between a small, a moderate, and a large change are still unknown. We used the data set of National Emphysema Treatment Trial consisting of severe and very severe chronic obstructive pulmonary disease patients, whose mean age was 64 years. Changes from baseline to post-surgical 6-month follow-up were evaluated. The St. George's Respiratory Questionnaire was used as anchor: vertical bar Delta SGRQ vertical bar < 4, meaningless change; 4 <= vertical bar Delta SGRQ vertical bar < 8, small change; 8 <= vertical bar Delta SGRQ vertical bar < 13, moderate change; 13 <= vertical bar Delta SGRQ vertical bar, large change. We decided the final cutoff values for the SOBQ as medians of the three anchor methods. We also decided the range of cutoff values as the range of three values. In a cohort of surgically treated patients (N = 484), we propose value of 5 (range 5-6), 11 (range 9-15), and 16 (range 14-20) for the cutoff values between a meaningless and a small change (minimum clinically important difference), a small and a moderate change, and a moderate and a large change, respectively. In a cohort of medically treated patients, numbers of patients categorized according to Delta SGRQ scores were similar to those of the patients categorizes according to the Delta SGRQ (N = 480) or Delta Forced expiratory volume in 1 second (N = 425). We propose group-level cutoff values and range between a small, a moderate, and a large changes.