Just as a bias exists to publish positive—and not negative—results from clinical trials, our field favors reports demonstrating that an illness is more prevalent or has greater impact than previously documented. Take Alzheimer's disease. A few decades ago this was a rare presenile dementia. But because similar pathology was found in later-onset dementias, the diagnosis was extended to include these cases. This step made a very rare disease quite common, and it has culminated in studies showing that Alzheimer's disease affects half of all persons over 85. However, the neuropathological changes that are the sine qua non of Alzheimer's disease are found among very old persons without dementia. The gold standard for diagnosis is not a gold standard. Yet these high prevalence rates are cited when our field requests more funding for training, clinical care, or research.