RE: LFT’s coming to Lancashire4 Nov 2020 08:58
Taken from the comments, but it seems like someone knows about this test.
The lateral flow test has a PPA of 89.9% at 95% confidence interval.
In English this means that if they test enough people, and there is enough virus in the population they can say with 95% surety that the each time the test produces a positive test, 10.1% of those positive tests will be false positives.
Let's say there are 10% of the population with the virus
And 10,000 people as the trial states will take the test
Then there will be 1,000 positive tests from people who have the virus.
This is true
However this means that from the original 10,000, 10.1% will return a positive test but don't have the virus.
This will result in a 20.1% positivity rate (minus false negatives but this negligible).
What I'm pointing out here is that you sacrifice accuracy with speed.
So if you have a 10% chance of having the virus when you take the test, you have a higher chance of testing positive without having the disease, 10.1%
These tests only work when there is a high prevalence, ie when there are a significant number of the population with the virus.
If 80% of people have the virus 10.1% becomes a small fraction
This is why these tests are used primarily when they know somebody has an illness, ie test for prostate cancer
Hope that helps