2013 Articles

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

Hobart, Jeremy; Cano, Stefan; Posner, Holly; Selnes, Ola; Stern, Yaakov; Thomas, Ronald; Zajicek, John; Alzheimer's Disease Neuroimaging Initiative

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 5 675) 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 a 5 0.74), and validity (correlation with MMSE 5 20.70) were satisfied. Responsiveness (baseline to 12 months; n 5 145) was moderate to high (effect size 5 20.73). 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. Ó 2013 The Alzheimer’s Association. All rights reserved.