Annals of neurology
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Using different criteria for classifying patients into various stages of a disease can modify the stage-specific prognosis, even though the overall disease course remains unchanged. This is known as the "Will Rogers phenomenon," precluding the use of historical controls for treatment trials. We assessed whether the Will Rogers phenomenon may affect multiple sclerosis (MS) prognosis when applying different diagnostic criteria. ⋯ The use of different diagnostic criteria may generate spurious improvements in the medium-term prognosis of MS. This calls for caution in using historical controls for MS trials.