29 December 2010 3 Comments

100 Days of Sleep – Part 3: What Makes a Good Night’s Sleep?

When I started analyzing the sleep data, I was very interested to see if particular phases of sleep correlated more closely to how I felt the next day. Yesterday, I showed some ways the data could be simplified. Today, I’ll use the data to make a complete model.

To understand the relationship between each parameter, I performed a partial least squares (PLS) regression using the data. This is a fairly-high powered method of multivariate analysis that is particularly suited for large sets of variables. As an alternative, I could have reduced my variable set to those identified in yesterday’s post and used a simpler analysis method. But PLS is the best way to a robust model using all of the available data.

For the PLS analysis, I used SIMCA-P+ v.12.

Below is the PLS Loading Plot from my sleep data. The black items are the predictors (i.e., x-variables) while the red items are the predicted (i.e., y-variables). Similar to a PCA plot, the items furthest from the origin of the plot have the most influence. Once again, we see clustering of Total Z, Time in Light, and ZQ.

The analysis clearly demonstrates that Total Z and Time in Deep are the two factors that are most necessary to feel rested the following day.

With this information, I used SIMCA-P+ to construct a model based on the two sleep factors – Total Z and Time in Deep – to predict Day Feel. (I used only Day Feel 1, since it was representative.) The resulting model is shown below.

This plot shows the next day’s feel as a function of the minutes of total sleep I got (ranging from 3-9 hours) and the minutes of time in deep sleep. It clearly shows that Time in Deep is a very important factor. In fact, getting an extra 15 minutes of deep sleep is the equivalent to getting an entire extra hour of sleep!

What do I conclude from this?

  1. I have to get the right amount of Total Sleep AND Deep Sleep to have a good night’s rest.
  2. Getting extra Total Sleep is relatively straightforward (if not always easy). But, I need to figure out how to get adequate Deep Sleep!

Tomorrow, I’ll dive a little deeper (pun) into my Deep Sleep data, and post my next steps and outstanding questions.

3 Responses to “100 Days of Sleep – Part 3: What Makes a Good Night’s Sleep?”

  1. Julius Smith 1 January 2011 at 1:14 am #

    I have reached compatible overall conclusions based on checking my sleep breakdown every morning. My summary is that if I see at least half an hour of deep, and two hours of REM, I’m good to go. In fact, I find I can get up after only 5 hours of sleep if I hit those numbers (which can happen when I was sleep-deprived the previous night). A whole hour of deep actually makes me feel excessively rested and relaxed (hard to get going the next day). I am 57, and I think half an hour of deep is about average for my age. I feel I need about half an hour more than average for REM.

    By far the biggest disruptor of deep sleep I have found is alcohol. I can tolerate one beer or glass of wine, but two pints of beer, or two good-sized glasses of wine, and my deep-sleep tally can plummet to zero for the entire night. Coffee is not nearly as bad – when consumed late in the day it can delay sleep and cause more awakenings, but it does not disrupt the sleep cycle as badly, and I can pretty well compensate with more total Z time.

    In agreement with your data, I find I can always “top up” my REM by sleeping more in the morning, but there is little I can do about lost deep sleep, so I carefully limit my alcohol intake to protect it. It can also be damaged by eating a large dinner or eating too close to bedtime.

    My general feeling is that deep sleep is critical for feeling rested the next day, and REM is important for maximizing my problem-solving/work skills. (I’m an engineer.)

    Thanks for crunching the numbers and sharing the results!

  2. Michele Rizack 7 April 2011 at 1:11 pm #

    Hello there,

    I have read that most people have more deep sleep before midnight/1AM than after, for example if you went to sleep at 10PM versus midnight. Could you make an analysis of sleep phases as a function of actual clock time and see what shows up?

    Thanks for posting your numbers, it gives me ideas on what to do with my zeo data!


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