not reflect potential future variation across regions and states in other risk factors for dementia such as midlife hypertension and diabetes. Incidence of Alzheimer’s Dementia While prevalence refers to existing cases of a disease in a population at a given time, incidence refers to new cases of a disease that develop in a given period in a defined population — in this case, the U.S. population age 65 or older. Incidence provides a measure of risk for developing a disease. According to estimates using data from the CHAP study and the U.S. Census Bureau, approximately 910,000 people age 65 or older developed Alzheimer’s dementia in the United States in 2011, a number that would be expected to be even higher in 2022 if CHAP estimates were available for that year.261 The number of new cases of Alzheimer’s increases dramatically with age: according to estimates from CHAP, in 2011 the average annual incidence in people age 65 to 74 was 0.4% (meaning four of every 1,000 people age 65 to 74 developed Alzheimer’s dementia in 2011); in people age 75 to 84, the annual incidence was 3.2% (32 of every 1,000 people); and for age 85 and older (the “oldest-old”), the incidence was 7.6% (76 of every 1,000 people).261 A 2015 study using data from the Adult Changes in Thought Study, a cohort of members of a health care delivery system (Group Health Cooperative of Puget Sound (now Kaiser Permanente Northwest) in the Seattle area of Washington, reported similar incidence rates to the CHAP study.10 Because of the increasing number of people age 65 and older in the United States, particularly the oldest-old, the annual number of new cases of Alzheimer’s and other dementias is projected to double by 2050.262 Lifetime Risk of Alzheimer’s Dementia Lifetime risk is the probability that someone of a given age who does not have a particular condition will develop the condition during that person’s remaining life span. Data from the Framingham Heart Study were used to estimate lifetime risks of Alzheimer’s dementia by age and sex.A5,263 As shown in Figure 4, the study found that the estimated lifetime risk for Alzheimer’s dementia at age 45 was approximately 1 in 5 (20%) for women and 1 in 10 (10%) for men. The risks for both sexes were slightly higher at age 65.263 Differences Between Women and Men in the Prevalence and Risk of Alzheimer’s and Other Dementias Almost two-thirds of Americans with Alzheimer’s are women.224 Of the 6.5 million people age 65 and older with Alzheimer’s in the United States, 4 million are women and 2.5 million are men.224 This represents 12% of women and 9% of men age 65 and older in the United States.221 Women live longer than men on average, and older age is the greatest risk factor for Alzheimer’s.263-265 This survival difference contributes to higher prevalence of Alzheimer’s Prevalence 25 and other dementias in women compared with men. However, when it comes to differences in the risk of developing Alzheimer’s or other dementias for men and women of the same age (i.e., incidence), findings have been mixed. Most studies of incidence in the United States have found no significant difference between men and women in the proportion who develop Alzheimer’s or other dementias at any given age.10,77,265-267 Some European studies have reported a higher incidence among women at older ages,268-269 and one study from the United Kingdom reported higher incidence for men.270 Differences in the risk of dementia between men and women may therefore depend, in part, on age and/or geographic region.271-272 Other studies have provided evidence that any observed difference in dementia risk between men and women may be an artifact of who is more or less likely to die of other health factors before developing dementia. A study using Framingham Heart Study data suggested that men in the study appear to have a lower risk for dementia due to “survival bias,” in which the men who survived to age 65 or beyond and were included in the study were the ones with a healthier cardiovascular risk profile (men have a higher rate of death from cardiovascular disease in middle age than women) and thus a lower risk for dementia.264 Recent studies have supported the notion that selection bias contributes to reports of sex and gender differences in Alzheimer’s dementia.273 More research is needed to support this interpretation. Although differences in the rates at which men and women develop Alzheimer’s or other dementias do not appear to be large or consistent, the reasons men and women develop dementia may vary. These differences may be based in biology such as chromosomal or hormonal differences related to reproductive history274 (i.e., sex differences) or in how social and cultural factors are distributed among or are experienced by men and women (i.e., gender differences), or the combination of the two.271,275 Gender differences may exist in the distribution of or even the effect of known risk factors for dementia, such as education, occupation, and health behaviors. For example, lower educational attainment in women than in men born in the first half of the 20th century may contribute to elevated risk in women, as limited formal education is a risk factor for dementia.276 This possibility requires more research, but evidence supports that greater educational