Stages in the natural history of lung cancer
lead time of screening
In this example, using lung cancer for which clinical trials
have demonstrated no efficacy for screening, the principle of
lead time is illustrated. Despite person A being diagnosed with
disease earlier than person B, they both die at the same time.
Thus, no decrease in mortality was gained by person A, only the
length of time during which he knew he was sick was increased.
Time with disease is extended which leads to the false impression
that early detection improves total survival.