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What is the Sleep Regularity Index?

May 9, 2024
5 minutes
Evidation Highlights
Health assessment and Evidation

The Sleep Regularity Index (SRI) is a measure used in sleep research to gauge the consistency and regularity of a person’s sleep-wake schedule. It’s calculated based on factors such as bedtime, wake-up time, and sleep duration.

Researchers and healthcare professionals use the SRI to assess the quality and stability of an individual’s sleep-wake cycle. Irregular sleep patterns have been associated with various health issues, including mood disorders, impaired cognitive function, and cardiovascular diseases.

A higher SRI means that a person has more consistent or regular sleep patterns, while a lower SRI suggests more variability or irregularity.

Understanding your Sleep Regularity Index can help you make choices that improve your sleep schedule and overall well being. That’s why our team of data scientists went to work to deliver this valuable insight to our members.

How we calculate your sleep regularity index

SRI can be calculated in different ways. Evidation uses the probability that you are in the same state (awake or asleep) at any two times 24 hours apart.

To explain this, we have to get a bit technical. But hang in there, it’s worth it! 

To get the most accurate picture possible, we look at your sleep data to find the time you went to sleep and the time you woke up each day over a 30-day period.

We use that information to figure out the hours you were asleep or awake at the same time on 2 consecutive days (2 days in a row). The following chart is an example of sleep data over 7 days.  Each area from left to right represents 1 hour of 1 day. When the person was asleep, the area is filled in blue.

bar graph showing hours an individual was asleep over a 7 day period
When a person was asleep over a period of ~7 days

For each hour of the day, we calculate how likely you are to be in the same state (awake or asleep) on consecutive days. We then average the values across all hours in the day to get your SRI.

As SRI is just a number, we provide a more detailed view of your sleep patterns through the daily sleep profile. The daily sleep profile is a plot of your likelihood to be asleep throughout the 24 hours of the day. The x axis (the horizontal line) is the time, and the y axis (the vertical line) is how likely you are to be asleep at that time.

Bar graph showing a person's likelihood to be asleep at specific hours throughout the night.

Very simply, the higher the bar, the higher your likelihood to be asleep. The lower the bar, the lower your likelihood to be asleep, in other words, the higher your likelihood to be awake. 

Middle-sized bars are for more “uncertain” times of the day when you’re neither very likely to be asleep nor very likely to be awake. It’s super important to be mindful of these times as this is when your sleep is the most inconsistent.

For many individuals, the daily sleep profile will look somewhat similar:

  • it will be close or equal to 100% in the night time, between midnight and 6am, when they’re most likely sleeping 
  • it will be close or equal to 0% in the day time, between 9am and 9pm, when they’re most likely awake, going about their day

The most interesting part is what happens between the high probability and low probability zones!

  • people who are highly regular sleepers have more “all or nothing” profiles—at a certain hour they go from being awake 100% of the time to asleep 100% of the time 
  • other people will have a pretty gradual decrease/increase in probability to be asleep: these are the more irregular sleepers   


Bar graph showing the Daily Sleep Profile for a very regular sleeper
Daily Sleep Profile for a very regular sleeper (SRI = 99%)


Bar graph showing the Daily Sleep Profile for a very irregular sleeper
Daily Sleep Profile for a very irregular sleeper (SRI = 53%)

It’s important to identify these “uncertain times” where your sleep is not regular. This is where you can work to move towards a more regular sleep schedule. Remember, going to bed and waking up at around the same time each day helps keep you healthy and well rested.

How do I interpret my Sleep Regularity Index?

The Sleep Regularity Index is defined as “the probability for an individual to be in the same state (awake or asleep) at any two times 24 hours apart”. So, if your Sleep Regularity Index is 92, it means that there’s a 92% chance that you’ll be awake or asleep at the same time each day.

Generally speaking, a Sleep Regularity Index in the 90s or above is considered good and healthy.

 How do I get my Sleep Regularity Index?

In order to receive a sleep regularity score from Evidation you must do the following:

  1. Use a wearable device that logs sleep and connect it to your Evidation app. Make sure you enable sharing of sleep data when you connect your device.
  2. Wear your device while sleeping for at least 20 of the last 30 days. We need to see your observed sleep in order to accurately calculate the Sleep Regularity Index. Too few data points will make our calculations inaccurate.

Click here to learn more about connecting your device.

How often will I get my Sleep Regularity Index?

If you follow the steps above, we’ll send your Sleep Regularity Index to your My Health tab monthly. 

Remember to regularly sync your device with Evidation. This guarantees we’ll have the most accurate information for providing you insights like the Sleep Regularity Index.

Health insights on Evidation

We’re constantly adding new insight types to help our members learn more about their health and take control of their health journey. Keep a look out for additional insight types coming soon. 

Interested in seeing insights like this, but don’t have a device connected yet, Find out which devices are compatible with Evidation and how you can pair your device here

Don’t yet have the Evidation app? Download now on iOS or android. 

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