APOE and dementia: Among those with normal cognition, even if the sample is enriched with ApoE e4 carrier status, about 2300 subjects are required using the Clinical Dementia Rating scale (CDR) sum of boxes as an outcome, and 27,380, 8146 and 1237 subjects are required when the primary outcomes are psychometric test scores, the ADAS-Cog, MMSE, and RAVLT-delayed recall, respectively.