Application of generalizability theory confirmed lower reliability of the standard gamble than the feeling thermometer

OBJECTIVES: Recent studies suggest that rating clinical marker states (CMS) does not improve the measurement properties of the standard gamble (SG) and only slightly improves those of the feeling thermometer (FT). The poor intrarater (test-retest) reliability of CMS may explain their meager performance. Further, lack of interrater reliability may compromise the use of CMS in interpreting health state ratings. The aim of this study was to assess the reliability of CMS ratings for the SG and the FT. STUDY DESIGN AND SETTING: 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. RESULTS: 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). CONCLUSIONS: These results suggest that the markedly poorer reliability of CMS for the SG than the FT is driven largely by poor interrater reliability.