NHS SCREENING PROGRAMMES
The idea behind screening programmes seems sensible. the principle is that if you can diagnose a disease before symptoms develop it will be easier to treat successfully. This sounds sensible but it does not always hold true.
The trap that many people fell into is called Lead Time Bias
the NHS has very strict rules and methods for judgubg whether a screening test is effective or whether it just looks as though it is effective as a result of Lead Time Bias so
The idea behind screening programmes seems sensible. the principle is that if you can diagnose a disease before symptoms develop it will be easier to treat successfully. This sounds sensible but it does not always hold true.
The trap that many people fell into is called Lead Time Bias
- Imagine you have a disease that takes ten years to kill you, from day one to death
- Imagine also that symptoms develop after seven years, so survival time is three years
- If a new screening test is developed that can diagnose the disease two years earlier the survival time will be five years but there will have been no improvement in that person's health. the result will simply be that they will know about the disease for two years longer before dying.
the NHS has very strict rules and methods for judgubg whether a screening test is effective or whether it just looks as though it is effective as a result of Lead Time Bias so
- if you get an invitation from an NHS screening programme consider it carefully.
- if you get an offer of a screening test or an early diagnostic test from a private service put it int he waste paper basket