Fewer seniors are experiencing “cognitive impairment” across the country today compared with a decade ago, according to researchers at the University of Michigan Medical School.

The nationally representative study looked at 11,000 people aged 70 and above and found that, between 1993 and 2002, the rate of impairment decreased from 12.2% to 8.7%. Researchers can’t say why the numbers have gone down, but lead author Kenneth Langa, M.D., Ph.D., speculates that “education and wealth may be a big piece of the puzzle.”

Nearly three out of four seniors over the age of 65 had a high school diploma in 2003, compared to just more than half a decade previous, notes Langa, and the rate of seniors with a college degree rose from 11% to 17% during the same time period. The report can be found online in the journal Alzheimer’s and Dementia.