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Scientists estimate that at least 25 % of all people who are told that they have Alzheimer's disease actually suffer from some other problems that can be treated, such as depression. A definitive test for Alzheimer's would advise doctors whether or not to keep looking for the source of patients' memory losses. Just as important, researchers are testing drugs that may slow the process of mental deterioration in order for those treatments to work, however, doctors must give them before there is any memory failure.