More iAbra statistical nonsense
Following from the Telegraph at the weekend, I have now seen the data from iAbra for their 20 second "Holographic microscopy" saliva test being trialled at Heathrow.
Start here in the FT, then see below.
1/10
ft.com/content/e7a279…
In FT I said:
“we are in a pandemic, people are dying from the disease, and a company decides that it is reasonable to mislead us all to make their test look like the best thing available."
2/10
"Legally, they can probably get away with this, but there cannot be any consideration that this is morally acceptable.”
They have said my characterisation was “incredibly unfair”.
See what you think.
3/10
The product claim made by iAbra says:
Virolens®, a new screening device for COVID-19, can deliver results in just 20 seconds with 99.8% sensitivity and 96.7% specificity.
4/10
Sensitivity first
99.8% sensitivity means that if you had a 1000 people with Covid, it is positive in 998 of the people. iABRA has a different take on what sensitivity is.
Their sum which gives 99.8% is 156751940/157000000.
So what are these huge numbers?
5/10
They say they are “counts” of “virons” averaged across 3 samples. I presume they are counts of virus particles.
156751940 is the number from their machine. 157000000 is the expected number from some computation based on the replication rate (no further info given).
6/10
So the 99.8% relates to a quantity (viron count) measured in 3 artificial samples as a percentage of the value that they expected to see.
This is not an estimate of sensitivity but an assessment of measurement accuracy of their test
7/10
Specificity is worse.
Actually they call is Specitivity, so spelling is a problem too.
96.7% specificity means that of your sample of a 1000 people who are being tested for COVID but have nothing or other things, it is correctly negative in 967 of the people.
8/10
iAbra has a different take on what specificity is.
Their sum which gives 96.7% is 13232/13681
Again it is a ratio of a virus particle count to an expected value (doesn’t say how many samples).
Again it is an assessment of the measurement accuracy of their test.
9/10
If none of the clever people at iAbra know about sensitivity and specificity then they should not be working in this field.
If they do know, they are throwing sand in our eyes, which is morally indefensible.
What do you think?
10/10
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