Dr. Matt Walker

Sleep efficiency is simply calculated as of the total amount of time in bed, what percent of that time were you asleep?

So if I was in bed for eight hours and I slept for six hours, I would have a sleep efficiency of 75%.

Because two out of the eight hours, 25% of that time, I was awake.

An efficiency that is 85% or above, we typically classify as healthy sleep.

And we would like to see you there or perhaps a little bit higher.

If you have a lower sleep efficiency score than that, it usually means that you're awake too much of the time.

And we'll think about that and address that.

So that's one measure of the second Q of the QQRT.

That's quality.

But there's another measure that we can also use.

That measure comes back to the deep sleep that we spoke about and particularly the electrical quality of those brainwaves.

So you can have deep sleep and it can be of different qualities, electrical qualities.

You can have deep sleep that is immensely powerful with huge epic waves, or you can have deep sleep that still is classified as deep sleep, but it's a little bit more sort of anemic in its quality.

And you can't really measure that with these sleep trackers.

We have to use electrodes, and then we decompose the electrical brain activity using a fancy equation.

And that tells us what was the amount of sort of strength of activity, what we call electrical power, in that deep sleep regimen.

So that's another measure that we use for quality.

Next is regularity.

Regularity, and actually I should come back to quality.

For a long time in sleep science, we were using quantity as our major metric for predictability, meaning I look at your quality and does it predict your learning or your memory?