Abstract
Adjustments for lead and length time bias has been used when examining apparent survival advantages from screening procedures. However, these estimates depend on several assumptions and are modeled from malignancies that are fairly common and large cohorts are available. In smaller retrospective cohorts, adjustments themselves may be based on estimates that may not be biological nor statistically accurate, which can lead to divergent results as has been found in several recent studies of screening in Barrett's esophagus. Only a prospective randomized controlled trial can really determine the benefit though this may not feasible.