Putting the Alzheimer's cognitive test to the test I: traditional psychometric methods.

BACKGROUND: The Alzheimer's Disease Assessment Scale-Cognitive Behavior section (ADAS-Cog) is the most commonly used cognitive test in AD clinical trials. However, there are concerns about its use in early-stage disease. Herein we examine those concerns using traditional psychometric methods. METHODS: We analyzed ADAS-Cog data (n = 675) based on six psychometric properties: data completeness; scaling assumptions; targeting; reliability; validity; and responsiveness. RESULTS: At the scale-level, criteria tested for data completeness, scaling assumptions (item total correlations 0.33-0.59), targeting (no floor/ceiling effects), reliability (Cronbach's α = 0.74), and validity (correlation with MMSE = -0.70) were satisfied. Responsiveness (baseline to 12 months; n = 145) was moderate to high (effect size = -0.73). However, 8 of 11 ADAS-Cog components had substantial ceiling effects (range 32%-83%), and decreased responsiveness associated with low to moderate effect sizes (0.14-0.65). CONCLUSION: In our study, many patients with AD found large portions of the ADAS-Cog too easy. Future research should consider modifying the ADAS-Cog or developing a new test.