For example, if all the patients receiving a drug were over 85 and all the patients receiving an inactive placebo were much younger, it might appear the drug was working when, in fact, the populations were improperly matched, Gandy pointed out.
"We have known that we wanted populations to be as identical as possible, but we didn't really know of this specific phenomenon before," he said.
For more information on Alzheimer's disease, visit the Alzheimer's Association.
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