Table 5. Power for ADAS-cog outcomes in 18 month long trials of participants with dementia due to AD based on APOE ε4 carrier status.

To ensure an approximate power of 80% to 90% for the mixed model analysis, simulations show that for small effects of 0.25, typical to that of cholinesterase inhibitors, somewhat fewer than 400 patients per group are needed with a dropout rate of 40%, and for medium size effects of 0.45, somewhat greater than 100 per group are needed with a dropout rate of 40%. Enrichment based on APOE ε4 carrier status resulted in very small increases in statistical power. Simulation parameters included α=0.05, effect sizes of 0.25 to 0.45 with Chisquared random errors, and 40% dropouts with mixed model analysis for participants with missing data.

N per group	Effect Size	Apo ε4 %	Treatment group mean	Placebo group mean	Treatment group SD	Placebo group SD	Power mixed model
50	0.45	0.0	2.43	5.63	8.03	7.61	0.437
50	0.45	0.6	3.02	6.35	7.99	7.63	0.474
50	0.45	1.0	3.55	6.82	7.91	7.54	0.454
100	0.45	0.0	2.29	5.69	8.18	7.83	0.709
100	0.45	0.6	2.96	6.32	8.04	7.69	0.722
100	0.45	1.0	3.37	6.66	7.95	7.60	0.732
200	0.35	0.0	3.06	5.69	8.20	7.87	0.768
200	0.35	0.6	3.68	6.31	8.03	7.74	0.825
200	0.35	1.0	4.11	6.66	7.95	7.65	0.797
200	0.45	0.0	2.27	5.67	8.23	7.82	0.937
200	0.45	0.6	2.90	6.29	8.11	7.71	0.931
200	0.45	1.0	3.36	6.65	8.03	7.64	0.947
300	0.25	0.0	3.81	5.68	8.09	7.86	0.676
300	0.25	0.6	4.44	6.29	7.98	7.75	0.678
300	0.25	1.0	4.83	6.66	7.88	7.65	0.706
300	0.35	0.0	3.03	5.68	8.19	7.88	0.906
300	0.35	0.6	3.68	6.32	8.09	7.79	0.932
300	0.35	1.0	4.13	6.69	7.95	7.65	0.925
400	0.25	0.0	3.77	5.68	8.14	7.90	0.796
400	0.25	0.6	4.41	6.30	7.98	7.77	0.833
400	0.25	1.0	4.85	6.69	7.89	7.68	0.811
400	0.35	0.0	3.04	5.72	8.20	7.91	0.974
400	0.35	0.6	3.71	6.32	8.06	7.75	0.965
400	0.35	1.0	4.08	6.68	7.96	7.68	0.981