The study found evidence of a link between socioeconomic status (SES) and cognition, but only at baseline that is, the first test. Those with high SES performed better on the first assessment than those with middle SES, who in turn performed better than individuals with low SES. These differences, researchers said, could be linked to the effects of education, such as learned test-taking strategies and the possible direct effects of education on brain structure.

Researchers did find some demographic variation in rates of cognitive decline, with older participants declining faster than younger ones, and widows and widowers and those who never married declining faster than married individuals.

"The most consistent predictors of faster declines in cognitive functioning were being old and being single," the researchers wrote.

There are some potential limitations to the study, the researchers noted. Though few associations between socioeconomic status and the rate of cognitive decline were found in the AHEAD total cognition score, an association might emerge in other cognition domains not examined in the study. There was a greater drop-off during the follow-up period among participants with low socioeconomic status and among low-functioning individuals, possibly skewing results. Additionally, the researchers did not control for differences between groups in physical health.

In addition to Karlamangla, study authors included Dana Miller-Martinez, Carol S. Aneshensel, Teresa E. Seeman, Richard G. Wight and Joshua Chodosh, all of UCLA. Chodosh is also affiliated with the Veterans Affairs Greater Los Angeles Healthcare System.

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