Development and validity testing of an IPF-specific version of the St George's Respiratory Questionnaire.
BACKGROUND
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.
Yorke
Janelle
J
School of Nursing, Faculty of Health and Social Care, University of Salford, Salford, Greater Manchester, UK.
Jones
Paul W
PW
Swigris
Jeffrey J
JJ
D000368:Aged; D000959:Antihypertensive Agents / Q000627:therapeutic use; D000077300:Bosentan; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D054990:Idiopathic Pulmonary Fibrosis / Q000188:drug therapy / Q000503:physiopathology / Q000534:rehabilitation*; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D012720:Severity of Illness Index; D013449:Sulfonamides / Q000627:therapeutic use; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D014797:Vital Capacity
D000959:Antihypertensive Agents; D013449:Sulfonamides; D000077300:Bosentan