82: What your wearable sleep tracker is actually telling you

The consumer bio tracker industry is exploding, and many devices claim to measure sleep time, sleep stages, and sleep quality.  Devices that claim to improve sleep metrics are also emerging.  If you are reading this, I am guessing you’ve either bought or are considering buying a wearable consumer sleep tracker (CST).  

I have a sleep-tracking device of my own, the Oura ring.  I like seeing the “data” it puts out about my sleep in the morning.  But . . . is it accurate?  

The short answer is no, but we all know tech is evolving.  Rather than being sold as medical devices, most CSTs are currently described as “lifestyle/entertainment” devices that are not subject to United States Food and Drug Administration (FDA) oversight.  In fact, validation is often NOT conducted in head-to-head studies with simultaneous polysomnography (PSG, or attended sleep studies).  The technology for these devices is changing too fast to be systematically studied, so a healthy skepticism of accuracy is needed to avoid:

• Overestimation of the presence of a sleep problem (unnecessary anxiety)
• Underestimation of a sleep problem (delayed evaluation and treatment)

These devices are pretty good for determining when you fell asleep (sleep onset) and when you woke up to start your day (sleep offset).  Total sleep time may be fairly accurate to even slightly overestimated.  

Sleep staging is a different story. 

My Oura ring reports these sleep stages:  Awake, REM, Light sleep, and Deep sleep.  A few months ago (in 2023), the proprietary Oura algorithm changed and its report of my sleep stage percentages was suddenly different.  Noticeably different.  My deep sleep was reduced and there was also a drop in my REM sleep.  All because a new algorithm was uploaded into the platform . . . not because there was a real change in my sleep.  It was a nice reminder of the accuracy limitations.  

Since every device has different ways of measuring biological signals and different algorithms to interpret them, there are differences in sleep reports from one device to the next.  CSTs are tested on young people without any significant medical conditions or sleep problems.  The more you deviate from young, healthy, medication-free, and absence of sleep disorders, the less accurate your tracker becomes.  

Orthosomnia is a condition where individuals become overly preoccupied with achieving perfect sleep, often to the detriment of their actual sleep quality and overall well-being. Orthosomniacs often place too much faith in the accuracy of sleep trackers.

CSTs do NOT take the place of a formal sleep evaluation.  Recognize that companies selling CSTs have strong marketing agendas and claims– when you buy a CST you make a financial transaction.  Expensive or recognizable brands are not necessarily better ( more accurate) than others.  

There are definitely benefits to CSTs.

For one, CSTs elevate sleep as an important health metric.  They increase your awareness of sleep and engage you to understand how your total sleep time and sleep consistency affect your functioning the following day.  If you get feedback that something affected your sleep negatively, you are more inclined to improve that factor.  

Secondly, information from a CST is captured night after night, and evidence is emerging that variability in sleep quality and pattern can be significant.  CSTs give the wearer the ability to relate their sleep report to different stimuli, such as the effects of alcohol, changes in the sleep environment (noise, bed partner, hotel, etc.), or a shift in sleep pattern from travel across time zones.

If you’re looking for a number to describe accuracy, 70% is thrown out a lot.  I look for that number to improve over time, but not as fast as I want it to.  And I’m not even an orthosomniac.