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Lead time bias occurs if testing increases the perceived survival time without affecting the course of the disease. Lead time bias happens when survival time appears longer because diagnosis was done earlier (for instance, by screening), irrespective of whether the patient lived longer.
Lead-time bias occurs when the detection of a disease earlier does not alter the predetermined time of death (ie, discovering an incurable disease earlier and applying an ineffective therapy may seem to offer a survival benefit compared with therapies that are started later in the disease process).
Two other important forms of selection bias are lead-time bias and length time bias. Lead-time bias occurs in the context of disease diagnosis. In general, it occurs when new diagnostic testing allows detection of a disease in an early stage, causing a false appearance of longer lifespan or improved outcomes. [14]
Lead time bias refers to a distortion overestimating the apparent time surviving with a disease caused by bringing forward the time of its diagnosis.
Lead time bias occurs when cases who were detected by screening seem to have survived longer than diagnosed cases just because the disease was detected earlier, not because death was delayed. For example: Consider the following 2 scenarios of a patient who suffers from dementia since the age of 65:
Lead time (information bias)- the systematic error of apparent increased survival from detecting disease in an early stage. Length (information bias) - the systematic error from detecting disease with a long latency or pre-clinical period.
Lead‐time bias causes problems when the survival of patients with a particular disease is being compared between regions with and without screening programmes. In nephrology, it has become widely known as a problem of cohort studies comparing policies of early and late start of dialysis.
Lead-time and length-time bias are critical in analysing clinical trials involving time-to-event analysis. This article aims to simplify the concepts of lead-time and length-time bias and some solutions for controlling them.
Lead time bias is a bias that may be encountered in radiology literature on imaging detection of disease. Lead time is the time between detection of a disease with imaging and its usual clinical presentation.
Lead time bias refers to the artifact of apparent improved survival when measuring survival from the time a disease is detected. Even when there is no advantage to diagnosing or detecting a disease early, people will survive longer from the time of diagnosis when a disease is detected in an earlier, asymptomatic state.