Apple Watch data deemed unreliable by researchers due to sudden algorithm changes

Apple Watch ECG feature
Apple Watch ECG feature (Image credit: iMore)

What you need to know

  • Researchers say that using an Apple Watch to track data can be problematic because the data itself sometimes changes.
  • The changes happen when Apple updates the algorithms that are used to interpret the data Apple Watches collect.

Researchers say that they believe some of the health data collected by Apple Watches is unreliable, at least when used in a research setting. The reason is simple — the data Apple Watches collect often changes thanks to algorithm updates.

According to a new report by The Verge, PJ Onnela, associate professor of biostatistics at the Harvard T.H. Chan School of Public Health and developer of the open-source data platform Beiwe, is concerned that the data Apple Watches collect changes as Apple Watch algorithm updates are rolled out. Because Apple Watch doesn't surface the raw data to researchers, this inconsistency means that they can't trust the information they're being provided.

The issue is best shown by a test carried out a few months apart, both relating to the same data collected during the same timeframe. But because watchOS updates had made changes to the way Apple Watch interprets the raw data from its sensors, the results also changed.

So, they checked in on heart rate data his collaborator Hassan Dawood, a research fellow at Brigham and Women's Hospital, exported from his Apple Watch. Dawood exported his daily heart rate variability data twice: once on September 5th, 2020 and a second time on April 15th, 2021. For the experiment, they looked at data collected over the same stretch of time — from early December 2018 to September 2020.

While there was some expectation that the two exports would see some data differences, the results were still striking. If the same data isn't actually the same data depending on when it's extracted, how can it be trusted?

Put simply — it can't, whether you're using the latest and greatest Apple Watch Series 6, or not.

You can read the full report over on The Verge along with more input from other researchers.

Oliver Haslam

Oliver Haslam has written about Apple and the wider technology business for more than a decade with bylines on How-To Geek, PC Mag, iDownloadBlog, and many more. He has also been published in print for Macworld, including cover stories. At iMore, Oliver is involved in daily news coverage and, not being short of opinions, has been known to 'explain' those thoughts in more detail, too.

Having grown up using PCs and spending far too much money on graphics card and flashy RAM, Oliver switched to the Mac with a G5 iMac and hasn't looked back. Since then he's seen the growth of the smartphone world, backed by iPhone, and new product categories come and go. Current expertise includes iOS, macOS, streaming services, and pretty much anything that has a battery or plugs into a wall. Oliver also covers mobile gaming for iMore, with Apple Arcade a particular focus. He's been gaming since the Atari 2600 days and still struggles to comprehend the fact he can play console quality titles on his pocket computer.