According to the police, the true positive rate for sniffer dogs is 80% - there is a 4 in 5 chance that an alert from a dog will result in the person having drugs or having recently been in contact with drugspic.twitter.com/4S004hPJwZ
Epidemiologist. Writer (Guardian, Observer etc). "Well known research trouble-maker". PhDing at @UoW Host of @senscipod Email gidmk.healthnerd@gmail.com he/him
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According to the police, the true positive rate for sniffer dogs is 80% - there is a 4 in 5 chance that an alert from a dog will result in the person having drugs or having recently been in contact with drugspic.twitter.com/4S004hPJwZ
So what's the true negative rate i.e. the chance that someone who DOESN'T get stopped DOES have drugs?
Well, this is extremely hard to know. Some research suggests it is close to 0% (!), because huge numbers of people get into music festivals with drugs But let's assume it's better, maybe at the same 80% figure we're using abovepic.twitter.com/BzKXWM1nBl
So let's say that 100 people turn up to a music festival. Of these, 5 have drugs on them and 10 have recently been in contact with drugs
For this type of test, we usually make a 4x4 grid to represent the rates of true and false positives, like so we can fill in the numbers at the end of the right straight uppic.twitter.com/RnDHZ9Ormf
Now, our true positive rate - taken from the police - is 80%. That means that out of our 15 "has drugs" people, we'll identify 15*0.8 = 12 correctly, and 15*0.2 = 3 incorrectly, like sopic.twitter.com/e2SFzTJ6aY
So far, all well and good. Lots of people correctly identified, not that many missed. Very few "false negatives" But wait, there's more
'Doesn't has drugs' is, in a fit of irony, what you would say if you had LOTS of drugs.
James I'm trying to work out specificity and sensitivity here stop talking about drugs
Well there goes my grammar joke right down the, uh, drugs hole.
From what I've heard, every hole is the drugs hole
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