Fig. 5

Statistical power against trial duration: plots showing the relationship between the statistical power of the ADAS-CogIRT and the ANCOVA methodologies and duration of clinical trials for hypothetical treatment levels of (a) d = 0, (b) d = 0.2, (c) d = 0.5, and (d) d = 0.8. The sample size was fixed at 400 patients. ADAS-CogIRT Alzheimer’s disease assessment scale-Cognitive subscale scoring methodology based on item response theory, ANCOVA, analysis of covariance