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.
KEY MNEMONIC:
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.
Lead-time bias is due to early detection. Remember the "d" in lead is for early detection.
Reference:
Figures are from-- and longer (but not necessarily clearer) explanations can be found here: http://ecp.acponline.org/marapr99/primer.htm
Content on this page has not been checked for accuracy. The author's credentials have not been confirmed. Always use multiple peer-reviewed scholarly sources and good clinical judgement in your decision making.
Create an account for FREE to remove ads and access features including browsing history, favorites and private notes.