The Accuracy of The Oura Ring

In this article, we’ll walk you through the reliability of the Oura Ring. We’ll then introduce you to several research studies that have been conducted featuring Oura, to reveal how well the Oura Ring stacks up against medical-grade technology and standards.

Form & Function 

1. Measuring From the Finger

Unlike other wearables, Oura measures changes in your blood pulse volume from the finger instead of the wrist. If you recall the last time you went to the doctor, you may remember having your pulse taken from your finger and not your wrist—ironic? Indeed, there’s a reason for this. The arteries on the palm side of your finger are closer to the surface and larger than the capillaries found in your wrist, which permits for more intimate and precise measurement. Measuring directly from the arteries in your finger also allows Oura to capture your pulse signal as it leaves the heart, rather than on a delay on the return. Keep in mind that wrist oriented wearables are heavier and more likely to move, thereby exposing them to surrounding temperature. The Oura Ring in comparison, has a minimal profile and can nimbly follow skin temperature changes as its NTC (negative temperature coefficient) temperature sensor remains in close contact with your skin 24/7. 

Additionally, your fingers are in the furthest part of your peripheral vascular system, where within-day temperature variations are strongest. The wide range of fluctuation drawn from your skin temperature turns out to be very informative. These variations reflect your body's fine-tuned temperature regulation system that strives to keep your core body temperature stable by redirecting heat out through your skin over the course of the day. Your body changes this "heat redirection" in particular ways depending if you're healthy or sill, male or female, asleep or awake, etc. *Below, we provide more details on Oura's temperature detection. 

2. Designed with Top Sensors in Mind

Oura uses infrared light photoplethysmography (PPG), which penetrates deeper than green light LEDs found in the majority of wearables. Oura’s PPG sensors are similar to those found in select hospital devices, which are used to monitor heart rate. PPG operates by sending infrared light through LEDs to directly measure blood volume changes. Light is then received by these same PPG sensors via a photodiode (also known as a 'light detector'). The amount of light absorbed is directly proportional to the volume of blood found in your finger. Because Oura samples 250 times per second, this consistent capturing of pulses of light through your arteries accurately reflects your heart’s activity.

Additionally, the Oura Ring has LEDs positioned on both sides of your finger, allowing for the clearest signal to be picked up. To compare, most watch wearables are only able to offer a single-sided light source. 

3. Temperature Derived Directly from Your Skin

Oura is one of few wearables that measure temperature directly against your skin, rather than estimating it from the surrounding environment. Oura monitors changes in your skin temperature 24/7 to develop a strong, individualized baseline; however, Oura only reports on your nighttime values since there are multiple confounding factors present during the day, all of which can alter your temperature quite frequently and inconsistently. This “noise” can make data challenging to interpret, especially considering that simple lifestyle factors such as drinking a glass of water will likely cause variations. At night, your skin temperature is also closely related to your core body temperature. This allows Oura to offer an authentic snapshot of what’s going on internally—without the invasive procedures typically required to do so.

Oura tracks your nighttime skin temperature using an NTC (negative temperature coefficient) temperature sensor, which is able to detect changes as small as 0.05° C. Sampling is taken every minute throughout the course of the night. On top of that, our algorithm selects values that are most likely to correlate with core body temperature, with consideration of specific patterns of increase, decrease, and stability therein.

Keep in mind that Oura displays body temperature relative to your personal baseline. This means that Oura will show how much higher or lower your temperature is compared to your average (e.g. +0.1 °C/°F) rather than revealing absolute values (e.g. 36.5 °C / 99.5 °F). 

Oura matches the performance of research-grade temperature sensors (finger iButtons) > 99% of the time under lab conditions and 92% of the time under real-world conditions. At the bottom of this article, you can find more specifics on the accuracy of Oura's temperature data, if interested!

Studies & Validation

1. Validated Against the Sleep Lab Golden Standard: Polysomnography (PSG)

The Finnish Occupational Health Institute was able to validate the Oura Ring against the gold standard of sleep laboratory tests—polysomnography (PSG). PSG tests are considered top-of-the-line since they capture as much data as possible relative to sleep parameters. These markers include brain activity via electroencephalogram (EEG), eye patterns, muscle movement, and heart rate data derived from both electrocardiogram (ECG) and photoplethysmography (PPG).

The study concluded that “the Oura Ring provided unbiased and relevant data on sleep patterns,” including total sleep, sleep onset, and sleep stage breakdowns. Further, it noted that “the Oura Ring reached comparable performance levels to the best scientifically validated alternative methods to Sleep Lab measurements”. Meaning, Oura is able to provide valuable sleep data without the discomfort of lab instruments that would otherwise be required to collect the same degree of sleep analysis insights.

2. Heart Rate Variability and Resting Heart Rate Validation 

In a study of 49 healthy subjects performed by Oura’s Science Team, a near-perfect squared correlation (r²=0.996) for resting heart rate (RHRIcon_Heart.png) and an extremely good fit (r²=0.980) for heart rate variability (HRVIcon_HRV.png) was found between the Oura Ring and a medical-grade ECG (electrocardiogram) device when measuring for nighttime RHR and HRV.

If you’re unfamiliar with r², it’s the gold standard in statistics for assessing how well two variables correspond with one another. r² ranges from 0 to 1, and the closer the value is to 1, the more accurate the correspondence between two variables is. Because the r² values concluded from this study were both close to 1, this means that the RHR and HRV values presented in your Oura app thoughtfully resemble those produced by an ECG (electrocardiogram), the medical-grade standard for measuring the electrical activity of one’s heartbeat.

Here’s what the results looked like in the raw data produced:

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Observing how tightly the bolded black dots in the graph fall alongside the solid black line is an indication of how well the data produced by the Oura Ring held up against the ECG.

3. Respiratory Rate Validation

Oura’s Data Science Team recently completed a research initiative that compared Oura’s PPG-derived respiratory rate to an electrocardiogram (ECG)-derived method. An electrocardiogram, as mentioned above, is a test completed in a medical setting that measures the electrical activity of your heartbeat. Because respiration is difficult to directly measure without invasive or intrusive sensors, ECG-derived respiratory rate is a well-established practice that has been consistently used and identified as highly reliable.

You can find more specifics on the study design and partnership with Duke-NUS Medical School and the National University of Singapore here, but to sum things up, the Oura Ring was shown to be accurate in tracking overnight respiratory rate with an average error of less than 1 breath per minute (0.71 bpm). This means that respiratory rate measurements collected from the Oura Ring varied on average, by less than 1 breath per minute, in comparison to respiratory rate measurements collected from the ECG-derived method. This conclusion held true across the full range of respiratory rates, from high (>20) to low (<14), observed in the pool of 43 healthy, young adults that took part in the study. These results classify the Oura Ring as a valid tool for measuring average nighttime respiratory rate, on par with the ECG-derived method.

4. Body Temperature Validation

Most recently, our team completed an internal validation study of the Oura Ring's NTC (negative temperature coefficient) temperature sensor. Oura's task force of employees, data scientists, physiologists and engineers selected finger iButton sensors as the research-grade tool to evaluate Oura's performance against and were able to validate the ring's temperature sensor under both lab and real-world conditions. 

The data collected and confirmed under both conditions showed that Oura's temperature sensor matches research-grade performance under lab conditions, remains precise in real-world conditions and reflects changes in your physiology, not your environment. Each of these findings are further broken below.  

• The Oura Ring's temperature measurements matched the performance of research-standard iButtons as precisely as 0.13°C, every minute. 

• 16 individuals who wore both iButtons and Oura Rings for a week were able to show that Oura continued to match the performance of iButtons (r² > 0.92) throughout their full spectrum of life events including exercising, showering, cooking, working, etc. 

• In an analysis that included iButton sensors worn on the finger, as well as an 'environmental sensor' that traveled with these same 16 participants, the results revealed that while the Oura Ring and finger iButton match at 92% (r² > 0.92), temperature information from the finger is uncorrelated to the environmental temperature; 0.1% (r²=0.001). 

Please check out our blog post for a deeper dive into the protocols for each condition, as well as a more detailed scope on the findings and future implications.  

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Stay tuned for more research validation studies! Oura is always working hard to make the algorithms behind your insights even stronger.

Please stay up to date with the research branch of our blog, The Pulse, for news on the most recently published studies and results managed by our Science Team.

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