A systematic error introduced when followup does not begin at comparable stages in the natural history of the disease. Lead time bias can occur in comparisons of survival rates for conditions such as cancer when allowance is not made for the stage of the disease when diagnosis was made and treatment begun. Thus, early diagnosis of cases in a screening program and early treatment may or may not influence the survival rate. It may merely mean that the presence of the disease is known for a larger proportion of the person's lifetime.
Subjects: Public Health and Epidemiology.