Two similar studies in patients with chronic obstructive pulmonary disease (COPD, n = 91) and in patients with gastroesophageal reflux disease (GERD, n = 112) provided data for this analysis. Patients rated three different CMS (mild, moderate, and severe disease) twice several weeks apart. We used generalizability theory to calculate reliability coefficients.
Test–retest reliability for CMS ratings was higher for the FT compared to the SG (COPD: 0.86 vs. 0.67; GERD: 0.86 vs. 0.67). Interrater reliability was much higher for the FT compared to the SG (COPD: 0.78 vs. 0.46; GERD: 0.71 vs. 0.26).
These results suggest that the markedly poorer reliability of CMS for the SG than the FT is driven largely by poor interrater reliability.