They aren't clear what they mean by "97% accuracy". Does that mean 97% of people with arrhythmia are correctly diagnosed, or 97% of people are correctly diagnosed or not-diagnosed? If it's the latter, it's not very helpful at all. The number of people in the general population with arrhythmia is significantly less than 3%, so if this Apple Watch test says you have arrhythmia it is far more likely to be a false positive than a true positive.
Here, 97% accuracy refers to a c-statistic (area under the ROC curve) of 0.9740. An example operating point would be 98% sensitivity with 90% specificity.
For reducing false positives, rather than starting with the general population, it'd be natural to start with a higher risk sub-group, e.g., people with a high CHA2DS2-Vasc score.
Earlier this week, Circulation published a review screening for atrial fibrillation:
circ.ahajournals.org/content/135/19/1851.full?ijkey=StzSPk8eljGaP2G&keytype=ref
No, accuracy doesn't tell us anything about usefulness. If the test is cheap and it brings in people for a better test and thus saves lives it is useful. The only real danger is if people decide that since the watch says there is nothing wrong so they can ignore other symptoms.
It is something like chest pain: most of the time chest pain is not a symptom of a heart attack, but it is best indicator we have so you go to the emergency room when you have chest pain. Doctors there can evaluate your situation.
On a related note, I had a very rare stroke last week, only symptom: headache for 3 days.
The doctor sent me for a CT scan without any idea of what to look for. The only clue: it was not a migraine because I missed any neurological anomaly.
On the other hand, stroke prevalence is rare, 1.3% for men, and generally don't look like mine, and my kind is 2% of all strokes, it would have been completely weird to suspect it with such a low probability and such a non-specific evidence.
Long story short, I almost got sent home with an aspirin while I had an extensive cerebral veinous thrombosis.
Having spent a couple of days in a stroke ward over Christmas, the low prevalence of strokes should never be used as a reason not to test where possible.
I suspect a lot of people don't understand how serious and crippling - mentally and physically - a bad stroke can be.
If you're lucky a bad stroke kills you. If you're not lucky you lose a good part of your brain and motor function.
In practice this means you can be left unable to move some or all of your limbs, unable to talk, unable to hear, unable to understand what's happening around you, and perhaps unable to see.
It's no exaggeration to say that it can turn life into a nightmare.
Anything that makes this less common and less likely is a good thing.
Disagree. Note that both mammogram and colonoscopy frequency recommendations have both been reduced recently, both because the cost of screening and because of the consequences of false positives resulting in unnecessary medical intervention
That is a useful point, but not reason to disagree. In this case a cheap test that indicates you need a better test is useful. The risk of false positives needs to be considered, but that is for medical professionals. Even if the ultimate answer is for most people nothing more is done it still gets people into the doctor to explain what else they need to look for before a test is done.
