Lead Time Bias in Medicine and Psychiatry: A Concept Simply Explained.

Screening for a disease typically results in earlier diagnosis and hence longer life lived with the disease. Earlier diagnosis permits earlier intervention, which is good if it improves functioning and quality of life from an earlier time point, and if it improves the course and outcome of the disease. However, for diseases that are benign, those that are relentlessly progressive, and those that arise late in life, earlier diagnosis and earlier intervention may not meaningfully change course and outcome. In such situations, the early detection and longer life lived with the disease can incorrectly suggest that the screening and early intervention prolonged survival. Expressed otherwise, longer survival may merely be an artifact of starting measurement earlier. This artifact is known as lead time bias. Lead time bias has long been recognized for many medical conditions, including cancers. In psychiatry, lead time bias is clearly associated with survival in dementia, and has recently been investigated in the context of duration of untreated psychosis and outcome domains in schizophrenia. It is important to know about lead time bias because it may play an unrecognized role in shaping health policy and clinical practice.