Figure 3.

In this schematic, a screening tool has been applied to a hypothetical population of patients at intervals. Each patient is represented by a bar. The length of the bar represents the cancer-related survival of the patient. Length bias refers to the tendency of screening programs to identify patients with more favorable tumor biology (i.e., slower growth rates or less risk of metastasis), whereas patients with tumors with aggressive biology (rapidly growing tumors or those with a high risk of metastasis) may not be identified because of a short natural history until death. The finding of longer survival in patients identified through screening may not be related to the screening intervention—the benefit could lie in the natural history of these tumors. Modified from reference (29).