P2–308: Common rater errors when scoring the ADAS‐Cog

There is a growing concern that rater administration and scoring errors on the Alzheimer's Disease Assessment Scale-Cognitive subscale (ADAS-Cog) may be masking positive drug effect in some Alzheimer disease trials (Kobak, 2010; Schafer et al., 2011). Identification of key problem areas for raters may inform development of training programs so that raters can more skillfully perform the ADAS-Cog and thus minimize the risk of masking positive drug effects. This study examined rater performance on an ADAS-Cog training exercise and identified common rater errors when scoring the ADAS-Cog. A total of 326 raters from 4 AD clinical trials were selected to participate in a standard ADAS-Cog training program based on their reported educational status and experience with the measure. This training program included a 1 hour didactic session that reviewed the standard ADAS-Cog administration and scoring guidelines. The didactic session was followed by an evaluation exercise where raters were required to score a video-recorded ADAS-Cog administration. Raters' scores were compared to the criterion scores established for the video-recorded administration. Preliminary analyses indicated that 95% of the raters made at least one error rating the video-recorded ADAS-Cog; 17% (1 error) 29% (2 errors), 24% (3 errors), 12.5% (4 errors), and 12.5% (>5 errors). On average the group made 2.7 errors in scoring the video-recorded administration, which impacted the ADAS-Cog total score by ±1.2 points. Errors were identified in all ADAS-Cog subtests, with more frequent errors made on Remembering Test Instructions, Word Finding Difficulty, Comprehension, and Spoken Language Ability. Although raters were experienced administering the ADAS-Cog and were provided with training, most made at least 1 error on the ADAS-Cog training exercise. The errors committed by raters impacted the ADAS-Cog total score to varying degrees, which reaffirms the concern that rater errors may be masking true trial outcomes. Raters had greater difficulty rating items that involved clinical judgment, such as the language-evaluation items of the ADAS-Cog. Raters are likely to benefit from more substantial training and ongoing monitoring programs for these items.

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