So, according to this, the false positive rate for the Apple Watch in detecting atrial fibrillation is 0.04% (99.6% correct) This means that, on average, Apple Watches will be wrong more than 80% of the time Sound counterintuitive? This is the issue with population screeninghttps://twitter.com/statnews/status/1040273579391242242 …
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It's actually fairly basic maths The population prevalence for atrial fibrillation is about 1%
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Assuming that the false negative rate is 0% (this is pretty close, it was actually 2%), in a sample of 1000 people you'll get 10 with AF who will receive the correct diagnosis
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Now, the false negative rate is 0.04% So, in the remaining 990 people who are tested, 40 will receive positive results
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Keeping track, that means 4 out of every 5 people who are diagnosed using this app will be diagnosed incorrectly
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And remember, these people will then likely go on to receive unnecessary tests, interventions, and potentially medications Some of them will probably die
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This is why population screening is a fine art Even if your test is FANTASTIC, you have to be really damn careful Because otherwise you can KILL PEOPLE
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P.S. just in case this wasn't elucidated well above - 1% prevalence means that 10 in 1,000 people have the disease and AF=atrial fibrillation
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P.P.S - As has been pointed out, I got my simple maths incorrect here Serves me right for being overconfident! The true negative identification should be 4, thus the watch is only wrong ~1/3 of the time Still a fascinating phenomenon
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Replying to @GidMK
Even if it is wrong ⅓ of the time that is still a huge number. That’s a lot of people running to a cardiologist getting tested.
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Yeh that's why I left it up. Also, I used a high prevalence estimate, using a more conservative estimate it comes out as closer to the 80% again. The fewer people have AF, the worse the Apple Watch is
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