experts on aging said the studies also confirmed something they had suspected but had had difficulty proving: that dementia rates would fall and mental acuity improve as the population grew healthier and better educated. The incidence of dementia is lower among those better educated, as well as among those who control their blood pressure and cholesterol, possibly because some dementia is caused by ministrokes and other vascular damage. So as populations controlled cardiovascular risk factors better and had more years of schooling, it made sense that the risk of dementia might decrease. A half-dozen previous studies had hinted that the rate was falling, but they had flaws that led some to doubt the conclusions.