To test the reliability, validity and responsiveness of the 13-item Shortness of Breath with Daily Activities (SOBDA) questionnaire, and determine the threshold for response and minimal important difference (MID).
6 week, randomised, double-blind, placebo-controlled study.
40 centres in the USA between 29 October 2009 and 1 July 2010.
Primary and secondary outcome measures
547 patients with chronic obstructive pulmonary disease (COPD) were enrolled and 418 entered the 2-week run-in period. Data from the run-in period were collected to test internal consistency, test–retest reliability, convergent validity and known-groups validity of the SOBDA. Three hundred and sixty six patients were randomised 2:2:1 to fluticasone propionate/salmeterol 250/50 µg, salmeterol 50 µg or placebo, twice daily. Results from the SOBDA questionnaire, Patient Global Assessment of Change Question, modified Medical Research Council Dyspnoea Scale (mMRC), Clinician Global Impression of Dysponea Severity (CGI-S), Clinician Global Impression of Change Question and Chronic Respiratory Disease Questionnaire self-administered standardised version (CRQ-SAS) were evaluated; spirometry and safety parameters were measured. Study endpoints were selected to investigate the cross-sectional and longitudinal validity of the SOBDA questionnaire in relation to the clinical criteria.
Internal consistency of the SOBDA questionnaire (Cronbach α) was 0.89. Test–retest reliability (intraclass correlation) was 0.94. The SOBDA weekly scores correlated with the patient-reported and clinician-reported mMRC, CGI-S and CRQ-SAS dyspnoea domain scores (0.29, 0.24, 0.24 and –0.68, respectively). The SOBDA weekly scores differentiated between the responders and the non-responders as rated by the patients and the clinicians. Anchor-based and supportive distribution-based analyses produced a range of the potential values for the threshold for the responders and MID.
The 13-item SOBDA questionnaire is reliable, valid and responsive to change in patients with COPD. On using anchor-based methods, the proposed responder threshold shows a −0.1 to −0.2 score change. A specific threshold value will be identified as more data are generated from future clinical trials.
NCT00984659; GlaxoSmithKline study number: ASQ112989.