. Author manuscript; available in PMC: 2013 Dec 27.

Published in final edited form as: Brain Imaging Behav. 2012 Dec;6(4):10.1007/s11682-012-9166-3. doi: 10.1007/s11682-012-9166-3

Table 3.

Z-statistics for time, in the validation sample, from mixed models for cognition, controlling for age, education, gender, and APOE-4 alleles. Sample size needed per group to detect a 25 % decrease over 12 months, with 80 % power and alpha=0.05, two-sided

Clinical outcome	Time	N per group^a
ADAS-Classic	9.44	1230
ADAS-Modified	10.70	900
ADAS-Rasch	8.50	1409
ADAS-Tree	12.04	733
ADAS-Bifactor	10.26	1103
ADAS-Plus EF	10.61	883
ADAS-Plus EF & FA	11.81	547

Sample size calculations are based on the coefficient for year and the adjusted residual standard deviation from the full model. As such, they do not directly correspond to the z-statistics