Lead-time bias and Length-time bias both cause overestimation of survival duration.
Lead-time bias: Overestimation of survival duration due to earlier detection by screening than clinical presentation.
Length-time bias: Overestimation of survival duration due to the relative excess of cases detected that are slowly progressing.
- Imagine all 12 cases below are the same disease. Instead of being seen as rapidly progressive 50% of the time, rapidly progressive disease is only detected in 33% of positive screens.
Remember:
Lead-time bias and Length-time bias both cause overestimation of survival duration.
KEY MNEMONIC:
Lead-time bias is due to early detection. Remember the "d" in lead is for early detection.
Length-time bias is due to slow cases being detected more often simply because they are slowly progressing. Remember the "g" in length is for slowly progressing.
See also:
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