Development and validity testing of an IPF-specific version of the St George's Respiratory Questionnaire
- 1School of Nursing, Faculty of Health and Social Care, University of Salford, Salford, Greater Manchester, UK
- 2Division of Clinical Science, St George's Hospital, University of London, London, UK
- 3Autoimmune Lung Center and Interstitial Lung Disease Program, National Jewish Health, Denver, Colorado, USA
- Correspondence to Jeffrey J Swigris, Autoimmune Lung Center and Interstitial Lung Disease Program, National Jewish Health, 1400 Jackson Street, Denver, CO 80206, USA;
Contributors Study conceptualisation: JY, PWJ, JJS; data analysis: JY, JJS; manuscript preparation: JY, PWJ, JJS.
- Received 19 March 2010
- Accepted 20 July 2010
Rationale The St George's Respiratory Questionnaire (SGRQ) is often applied to assess health-related quality of life in patients with idiopathic pulmonary fibrosis (IPF). Some SGRQ items will inevitably have weaker measurement properties than others when applied to this population. This study was conducted to develop an IPF-specific version of the SGRQ.
Methods Data from a recently completed trial that enrolled subjects with IPF (n=158) who completed the SGRQ and other measures were analysed at baseline and 6 months. There were four phases to the study: (1) removing items with missing responses and using Rasch analysis on retained items to identify fit and refine item response categories; (2) development of a new scoring scheme; (3) testing agreement between original and revised versions and testing construct validity of the revised SGRQ; and (4) rewording to finalise the IPF-specific version (SGRQ-I).
Results Items were removed due to missing responses (6 items) and misfit to the Rasch model (10 items); 34 items from the original 50 were retained. For certain items, disordered response thresholds were identified and corrected by collapsing response categories. A scoring algorithm was developed to place SGRQ-I scores on a scale with SGRQ scores. For any given outcome measure (eg, forced vital capacity (% predicted) and lung carbon monoxide transfer factor (% predicted), 6-min walk distance and patient-reported questionnaires), Pearson correlations were similar between pairs that included original SGRQ scores and corresponding pairs that included SGRQ-I scores. Internal reliability (Cronbach α) for each SGRQ-I component was comparable to the original SGRQ (Symptoms 0.62; Activities 0.80; Impacts 0.85).
Conclusions The SGRQ-I contains items from the original SGRQ that are the most reliable for measuring health-related quality of life in patients with IPF.
Funding Actelion Pharmaceuticals funded the performance of the underlying BUILD-1 trial which investigated the efficacy of bosentan in the treatment of idiopathic pulmonary fibrosis. No additional external funding was obtained. JJS is supported in part by a Career Development Award from the NIH (K23 HL092227).
Competing interests None.
Ethics approval This study was conducted with the approval of the ethical committees (or Institutional Review Boards) of each of the 29 participating centres. All patients gave written informed consent to participate in the study.
Provenance and peer review Not commissioned; externally peer reviewed.