Interpretation of quality of life scores from the St George's Respiratory Questionnaire

The aim of the study was to obtain the general population norms for the St. George's Respiratory Questionnaire (SGRQ), a specific questionnaire for respiratory diseases. The IBERPOC project was a cross-sectional study of representative samples of the general population aged between 40-69 yrs. The study sample was composed of 862 individuals. All participants considered as "probable cases" of chronic obstructive pulmonary disease (COPD) (n=460) were eligible to complete the SGRQ and among the rest of the nonprobable COPD participants (n=3,571), 10 individuals from each defined age and sex group were eligible (n=402). Weights were applied to restore general population representativity of the sample. Mean forced expiratory volume in one second (FEV1) predicted was 89.4% (SD=16.5%; range: 16-131%). Chronbach's alpha coefficients were >0.7 in the symptoms, activity and impact scales, and >0.9 in the overall scale. Symptom scale score was significantly higher among males (11.6 versus 7.8; p