Apple Watch Identifies SARS-CoV2 Infection and Predicts Diagnosis

Whereas presumably you had some symptoms that were ignored?

If I stand up, take a few deep breaths, and then rest my arm on a level surface I get high 90's right away. So i don't worry about the outliers (much).

That's pretty immaterial when discussing theoretical effectiveness. Obviously, getting wide use depends upon it getting packaged up into an app listed on the app store, and some sort of awareness push.

That needs to be done once, by the app's authors. For lateral flow tests, to have similar effectiveness, that means that literally every Apple watch wearer (just to assume a similar population size) needs to get themselves a supply of tests (and keep getting new tests when they run out), and remember to perform the test every day. That is a much higher hurdle to jump than getting this app onto people's watches (assuming their study is correct and can be independently verified!). I also expect the supply of test kits is not robust enough to handle that kind of demand.

> Now, if you're making the argument that the Apple Watch app would be easier to distribute, then you can read the parent's criticism as "sure, but only knowing after you've potentially spread it is not very useful."

Reducing spread potential by 24 hours when you've perhaps been spreading it for a week already isn't exactly a game changer, but it's still useful, especially if the only thing people have to do is install an app on their watch. Expecting everyone to obtain rapid test kits and test themselves daily is in general a non-starter.

Yes, to make these same predictions you'd have to do some statistics as described in the paper, but no special app is required.

(And that's why this finding is interesting: they have the data available from patients before they were sick, because every new Apple Watch records this data out of the box.)

Only if you're willing to share of course :)

Something that detects 10% of cases and is completely free (using a device people are wearing anyway) is valuable. You can be sure that some of these cases would have been missed by all the other tests, simply because not every one of these cases got any test at all.

Have you compared the HRV data from different devices? Have you compared the Apple HRV data and the data from other devices to a reference instrument, or confirmed that it meets some standard?

The Apple Watch is the reference instrument for this paper. It would be a scientific error to conceal that fact.

This isn’t about product endorsements, it’s about saying what laboratory equipment was used so that other scientists don’t have hidden confounds when they attempt to replicate.

It's not about whether you "have a need for sudden changes" or not, but whether the sympathetic or the parasympathetic nervous system has the upper hand. There are many reasons for why it could be one or the other, but they are usually roughly summarized as "physical or mental stress".

For instance, when you sit at your keyboard and respond to someone who is wrong on the Internet, that is likely to cause negative emotions and mental stress. This would increase sympathetic nervous system activity and as a result lower your HRV.

"Further, you can be as healthy as a marathon runner and have very low HRVs."

Marathon runners are not always equally healthy. They also get sick or stressed sometimes, and quite often they are under physical stress due to training a lot. That's why some of them observe HRV to get an indication of their readiness for high intensity training or competitions (e.g. Whoop, Garmin Recovery Advisor).

That means, just sitting at their keyboard their HRV could be high or low, depending e.g. on how well they recovered from a hard training run.