Objective: To produce an improved, COPD-specific version of the St. George respiratory questionnaire (SGRQ-C).
Methods: Five different steps were required: (1) Rasch analysis of the responses of 893 COPD patients to the St. George respiratory questionnaire (SGRQ) identified weaker items to be removed; (2) a scoring algorithm was produced using data from 1,036 patients; (3) validity of the new and original SGRQ was tested using data from the original validation study; (4) responsiveness was tested using data from a previously published trial; and (5) a reworded version (SGRQ-C) that no longer specified the recall period was administered to 63 pulmonary rehabilitation participants.
Results: Items were removed due to lack of response (n = 1), misfit to the Rasch model (n = 8), and disordered responses (n = 1). Another six items had disordered responses; this was corrected. Scores from the two versions differed slightly, so the scoring algorithm was revised to produce scores equivalent to the original. Intraclass correlation coefficient (ICCC) for the scores for original and new versions was 0.99. Correlations with other measures of disease were very similar to those obtained with the original. New and original scores for treatment effects were similar: difference, 0.1 ± 2.7 U (± SD). Baseline SGRQ and SGRQ-C scores were similar (ICCC, 0.95; 95% confidence interval, 0.92 to 0.97; mean difference, 0.9 ± 5.8 U). Change scores were similar (difference, 1.0 ± 7.3 U).
Conclusions: The SGRQ-C contains the best of the original items, no longer specifies a recall period, and produces scores equivalent to the original.