Lead-time Bias
Updated 2026-08-03
INTRODUCTION
English translation pending.
CORE DEFINITION
An epidemiological bias that arises when a screening test detects disease earlier without altering its course. Survival measured from diagnosis appears longer simply because the clock starts sooner, while the time from true onset to death is unchanged. The patient lives longer with the label, not longer in fact. The bias is corrected by measuring from randomization or disease onset rather than from diagnosis, and by using hard endpoints such as overall mortality instead of survival time after detection.
SCAFFOLDING EFFECT
Reduce cognitive load
- Clock choice: check which starting point your metric uses before crediting any improvement. - Endpoint audit: replace soft measures such as time-to-detection with hard outcomes. - Management check: ask whether earlier warning actually improved handling or only lengthened the worry.
Anchor fast decisions
Screening shifts the moment of detection earlier on the same timeline, so the interval from detection to a fixed endpoint stretches mechanically. No biological change is required for the number to improve. Because the measured quantity moves while the underlying process does not, the metric becomes an unreliable proxy, and any comparison between screened and unscreened groups is biased unless both are measured from the same starting point.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Lead_time_biasverified
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