In diagnostic studies, it is often reported that early detection of certain conditions can lead to improved outcomes, such as improved survival.  However, the fact that survival is usually measured from the point of diagnosis, it is not always possible to make accurate comparisons of the total survival (i.e. from onset of disease rather than from diagnosis).  Lead time bias refers to challenge of disentangling the effects of increased survival due to optimal treatment that was made possible by diagnosis, and apparent increased survival simply because the patient was followed from an earlier timepoint.  If the delay period (between early diagnosis and late diagnosis, usually when symptoms are apparent) is known, it is relatively easy to make adjustments to survival estimates.  However, in most cases the delay period is not properly known.  To solve this, diagnostic studies might be designed as randomised controlled trials, with patients either randomised to early testing or to a non-testing arm.  However, such designs would face ethical challenges, and would likely take many years to provide mature data.

How to cite: Lead Time Bias [online]. (2016). York; York Health Economics Consortium; 2016. https://yhec.co.uk/glossary/lead-time-bias/