Data and what to make of it

2 11 2009

I just downloaded data from my Dexcom and have been taking a look at it.  There’s so much data and so many different ways of looking at it; it’s hard to tell what to make of it.  There are a few items I like to focus on:

Modal Day screen

  • average blood sugar for the month
  • average blood sugar for the past 3 months
  • standard deviation

Glucose Distribution screen

  • % in range for the month
  • % in range for the past 3 months

Success Report screen

  • compare data montly
  • compare data quarterly

The average will tell me about what my A1c will be.  I use this chart and I have found that comparing my Dexcom average to this chart is very close to my actual A1c.

The standard deviation will tell me if I am doing too much of a rollercoaster.  Lower is better.  I will confess, mine is not as low as I would like, so I know that I need to level it out.

% in range is very important to me.  Knowing that I am in range 75% of the time is greatly empowering.  Knowing that I am 95% in range upon waking is even more empowering.  Of course, knowing I am only 50ish% in range after lunch tells me that I need to work on that area.

Comparing the data from month to month is great for trends.  I can see that my average in October was less that what it was in September, which is great.  I can also see that my average for the last quarter is lower than the previous quarter, so I imagine that my A1c will be lower as well.

Using the Dexcom software can be a little overwhelming (there’s so much more data available than I even mentioned), but if I focus on these few things, I feel like I have a pretty good handle on my diabetes control.


Average vs. Standard Deviation

6 08 2007

At my pump training a month ago, the pump trainers looked at my blood sugar history. They noted the standard deviation (std dev) was 46 and congratulated me on doing such a good job. Huh? I’m not a math major (that would be GiR), but I know that looking at the std dev alone is not the complete picture; just like looking at the average along is not the complete picture either. Take these examples:

  1. 50, 50, 100, 200
  2. 90, 95, 100, 105, 110

They both have the same average (100), but they have drastically different std devs. #1 has a std dev of 61 and #2 has a std dev of 7. Most glucometers output the average, but you can’t just take that by itself. Clearly a lower std dev indicates better control. However, you can’t just look at std dev by itself either.

  1. 90, 95, 100, 105, 100
  2. 205, 210, 215, 220, 225

We already know that #1 will produce an average of 100 and a std dev of 7. #2 also produces a std dev of 7. Does that mean it is good control? Not really. #2 has an average of 215! Not a place you’d want to be.

All I’m saying is to make sure you take both the average and the standard deviation into consideration. Both numbers together indicate your control. You want an average in your target range and a low standard deviation.

Note: This is the standard deviation calculator I used for this post. It’s a quick little tool that can help provide more data about your blood sugar.