Associations of cognitive performance and decline with APOE*4 reflect its being a risk factor for Alzheimer disease [35], and the corresponding moderate levels of heterogeneity are consistent with the relationship between APOE*4 and dementia being influenced by factors we did not control for in these analyses, such as race/ethnicity (which was controlled only in later analyses) and midlife vascular risk factors [36,37]. Here, APOE is linked to dementia.