A comparison of the original chronic respiratory questionnaire with a standardized version

The chronic respiratory questionnaire (CRQ), a widely used measure of health-related quality of life (HRQL) in patients with chronic airflow limitation, includes an individualized dyspnea domain (patients identify five important activities, and report the degree of dyspnea on a 7-point scale). Because the individualized domain is unwieldy in multicenter clinical trials, we developed a standardized version and tested its discriminative and evaluative properties.

We enrolled 51 patients who completed the standardized and individualized CRQ before starting a respiratory rehabilitation program, and again 3 months later. We calculated both cross-sectional and longitudinal correlations between the two versions and a number of other HRQL instruments, and tested the relative ability of the individualized and standardized versions of the CRQ to detect improvement with rehabilitation.

The results of the individualized questions suggested greater dysfunction (lower scores) than did the standardized questions both at baseline (3.18 vs 3.92, p < 0.001) and follow-up (4.62 vs 4.84, p = 0.051). The standardized dyspnea domain showed superior discriminative validity. While both techniques detected important, statistically significant improvement with rehabilitation (individualized domain mean change, 1.44; 95% confidence interval [CI], 1.11 to 1.77 [p < 0.001]; standardized domain mean change, 0.92; 95% CI, 0.61 to 1.24 [p < 0.01]), the difference in effect was substantial and statistically significant (mean difference, 0.52; 95% CI, 0.22 to 0.82; p = 0.001). The two versions showed comparable longitudinal validity.

A standardized version of the CRQ dyspnea domain improves the cross-sectional validity, maintains longitudinal validity, but reduces the responsiveness. By increasing sample size, investigators can use the more efficient standardized version of the CRQ without compromising validity.