Measuring respiratory symptoms in clinical trials of COPD: reliability and validity of a daily diary

N K Leidy, C C Sexton, P W Jones, S M Notte, B U Monz, L Nelsen, M Goldman, L T Murray, S Sethi, N K Leidy, C C Sexton, P W Jones, S M Notte, B U Monz, L Nelsen, M Goldman, L T Murray, S Sethi

Abstract

Background: Although respiratory symptoms are characteristic features of COPD, there is no standardised method for quantifying their severity in stable disease.

Objective: To evaluate the EXACT-Respiratory Symptom (E-RS) measure, a daily diary comprising 11 of the 14 items in the Exacerbations of Chronic Pulmonary Disease Tool (EXACT).

Methods: Qualitative: patient focus group and interviews to address content validity. Quantitative: secondary data analyses to test reliability and validity.

Results: Qualitative: n=84; mean (SD) age 65 (10) years, FEV1 1.2(0.4) L; 44% male. Subject descriptions of their respiratory symptoms were consistent with E-RS content and structure. Quantitative: n=188; mean (SD) age 66 (10) years, FEV1 1.2(0.5) L; 50% male. Factor analysis (FA) showed 3 subscales: RS-Breathlessness, RS-Cough & Sputum, and RS-Chest Symptoms; second-order FA supported a general factor and total score. Reliability (total and subscales): 0.88, 0.86, 0.73, 0.81; 2-day test-retest ICC: 0.90, 0.86, 0.87, 0.82, respectively.

Validity: Total scores correlated significantly (p < 0.0001) with SGRQ Total (r=0.75), Symptoms (r=0.66), Activity (r=0.57), Impact (r=0.70) scores; subscale correlations were also significant (r=0.26, p < 0.05 (RS-Chest Symptoms with Activity) to r=0.69, p < 0.0001 (RS-Cough & Sputum with Symptoms). RS-Breathlessness correlated with rescue medication use (r=0.32, p < 0.0001), clinician-reported mMRC (r=0.33, p < 0.0001), and FEV1% predicted (r=-0.17, p < 0.05). E-RS scores differentiated groups based on chronic bronchitis diagnosis (p < 0.01-0.001), smoking status (p < 0.05-0.001), and rescue medication use (p < 0.05-0.0001).

Conclusions: Results suggest the RS-Total is a reliable and valid instrument for evaluating respiratory symptom severity in stable COPD. Further study of sensitivity to change is warranted.

Keywords: COPD Exacerbations.

Figures

Figure 1
Figure 1
Higher-Order Factor Model for the E-RS. Confirmatory Fit Index (CFI)=0.958. Root Mean Square Error of Approximation (RMSEA)=0.073 (90% CI 0.050 to 0.096). Standardised Room Mean Square Residual (SRMR)=0.043. The E-RS is a derivative instrument, using the 11 respiratory symptom items from the 14-item EXACT. SOB, shortness of breath.

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