Lead time is the time between an easy diagnosis of a disease with improved screening, and when the disease would usually be diagnosed based on the presentation of symptoms. The bias occurs when the lead time is misconstrued to mean the average patient now experiences better outcomes. For example, if Huntington’s disease would usually be diagnosed at 50, and usually the patient will die at 65 this would be 15 years between diagnosis and death. Early genetic testing as a newborn could allow for 65 years of “survival” of the disease before the person dies at the usual age of 65.