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<0.01) and activity scale score was significantly higher among females (12.2 versus 14.6; p=0.04). In a multiple linear regression model, respiratory diseases (asthma and COPD) and FEV1 % over pred showed the strongest association with the SGRQ total score. Smoking, sex, age and education were independently associated with the total SGRQ score. These results indicate that individuals from the general population presented some of the problems that are important when measuring health-related quality of life in respiratory patients, and provide St George's Respiratory Questionnaire norms, a useful method for interpreting the St George's Respiratory Questionnaire score in a given patient or study samples.