Response rates were considerably higher in the U.S. study, and there were also differences in the methods for recruiting proxy respondents for sample members unable to respond directly.
Both studies also relied on respondents to provide information on health status, history, and behaviors.
Still, Dr. Reisa Sperling, a neurologist at Harvard Medical School who was not involved in the study, suggested that the findings "may have 'real-world' significance."
"I found the difference in education and wealth particularly interesting, and I would speculate that the differences in 'cognitive reserve' may explain some of the observed differences in cognitive performance," she said.
But another neurologist, Dr. Charles DeCarli, of the University of California, Davis, said the methodological differences between the U.S. and British data were a major weakness in the study. In particular, he cited the fact that the two studies administered their surveys in different ways. For example, in Britain, they were all conducted in person, whereas the U.S. study used both telephone and fact-to-face contacts.
DeCarli noted in an e-mail that the 70 percent of U.S. participants who responded by telephone could have written down the word lists to aid their memories.
He also pointed out that there could be national differences in the accuracy of self-reported health status.
DeCarli agreed that "increased health care services for chronic diseases may be beneficial" for cognitive function, but he added that primary prevention is even more important.
"Most of the cost of American health care relates to medical procedures and not preventive medicine," he said.
This article was developed in collaboration with ABC News.