MORGANTOWN, W. Va. — Just a few decades ago, it would have been impossible to track your sleep quality on a minute-by-minute basis. Of course, just like so many other areas of life, technology has changed all that. Wearable sleep tracking devices, such as the Apple Watch or Fitbit, are quite common nowadays. However, researchers from West Virginia University report some of these devices are much better at their job than others.
Joshua Hagen, director of the Human Performance Innovation Center at the WVU Rockefeller Neuroscience Institute, says he was motivated to conduct this research because there hadn’t been a proper third-party assessment of sleep tracker quality across various brands. He and his team set out to test the efficiency of eight commercially available sleep trackers.
FitBit for the win
In terms of measuring total time asleep, total wake time, and sleep efficiency, the study finds Fitbit and Oura are the top choices. All other tested devices overestimated or underestimated at least one of those three metrics.
Moreover, not a single one of the eight tested devices could accurately differentiate between and measure various sleep stages (REM or deep sleep) to the level that such readings would be helpful in comparison to an electroencephalogram (EEG).
“The biggest takeaway is that not all consumer devices are created equal, and for the end user to take care in selecting the technology to suit their application based on the data,” Hagen says in a university release. “Some devices are currently performing well for total sleep time and sleep efficiency, but the community at large seems to still struggle with sleep staging (deep, REM, light). This is not surprising, since typically brain waves are needed to properly measure this. However, when thinking about what you generally have control over with your sleep – time to bed, time in bed, choices before bed that impact sleep efficiency – these can be accurately measured in some devices.”
Five healthy adults took part in this study; two men (ages 26 and 41) and three women (ages 22, 23, and 27). Each person wore the sleep trackers for 98 evenings in total.
All of the trackers were better at assessing sleep/wake cycles than specific stages of sleep. Researchers say these findings suggest there is a “remarkably high degree of variability in the accuracy” from one brand’s sleep tracker to another.
“While technology, both hardware and software, continually advances, it is critical to evaluate the accuracy of these devices in an ongoing fashion,” Hagen adds. “Updates to hardware, firmware and algorithms happen continuously, and we must understand how this affects accuracy.”
Do the research before buying a sleep tracker
For what it’s worth, even Hagen himself is relatively confident such devices will only improve as time goes on. Right now, he uses four to five sleep trackers.
“I’m a big believer in living the research,” he explains. “I need to understand what the consumer sees in the smartphone apps, what the usability of the devices is, etc. Without that objective sleep data, you can only rely on how you feel when you wake up – and while that is important, that doesn’t tell the whole story. If your alarm goes off and you happen to be in a deep sleep stage, you will wake up very groggy, and could feel as though that sleep was not restorative, when in fact it could have been. It’s just not subjectively noticeable right at that moment.”
So, for consumers thinking about investing in a sleep tracker for themselves, researchers suggest taking some time to figure out which model will meet their needs the best.
“After accuracy, it comes down to logistics. Do you prefer a watch with a display? A ring? A mattress sensor? What is the price of each? Which smartphone app is most appealing? But again, that is if all accuracies are close to equal. If the price is right and the form factor is ideal, but the data accuracy is extremely poor, then those factors don’t matter,” Hagen concludes.
The study is published in Nature and Science of Sleep.