From the study linked [https://link.springer.com/article/10.1007/s40279-024-02066-5] (with acronym meanings added inline for readability):
"The lowest pulse arrival time standard deviation (PAT σ) at 2.0 times the standard deviation corresponded to 88.4% of the Region of Practical Equivalence (ROPE) for SDNN (Standard Deviation of Normal-to-Normal intervals), and 21.4% for RMSSD (Root Mean Square of Successive Differences). As the standard deviation of PAT increases, the equivalence between photoplethysmography-derived "heart rate variability" (PRV) and electrocardiography-derived heart rate variability (HRV) decreases for both SDNN and RMSSD. The width of the highest density interval (HDI), which encompasses 95% of the posterior distribution, increases with increasing PAT σ. This increase occurs at a higher rate for RMSSD than for SDNN."
So for "how accurate?", grossly and irresponsibly oversimplifying, the Apple method is roughly 90% accurate, and devices using the inferior method are roughly 20% accurate.
I would be really interested to know of any devices not locked down to Apple ecosystem that also use this approach, if anyone has any insight.
Not sure, but every video shows a huge graph with all of the watches on it, ranked by accuracy. If you just view the latest video you can get an idea of the best watches, or where a watch you might be looking at falls, then you can search for the specific video where he tests it to see specifics.
This is such a ridiculously wide divide that I'm surprised Apple hasn't used this, or something similar to this, as a marketing tactic. Imagine being able to say your medical insights are 70 percentage points more accurate than your competitors. I do understand this is apples to oranges, since these are often devices in a completely different price range, but still. I was surprised to hear this and I have been loosely following the medical wearables space for awhile.
I would imagine would be quite happy saying as little as possible about their sensors in their watches. It seems like their largest surface area for licensing litigation. Touting performance today is fuel in court tomorrow.
I mean, they'll definitely market it as 4.5x more accurate. Or, for nice round numbers, 5x -- and while we're within orders of magnitude it's not unreasonable to say "up to 10x more accurate."
Apologizes, you're correct. I vaguely remember reading they were "first" to get FDA approval for some feature, but if that were ever true, it is sorely outdated information. I fell for the hype, it seems.
Unfortunate that I can't delete or edit the post at this point.
So for "how accurate?", grossly and irresponsibly oversimplifying, the Apple method is roughly 90% accurate, and devices using the inferior method are roughly 20% accurate.
I would be really interested to know of any devices not locked down to Apple ecosystem that also use this approach, if anyone has any insight.