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:
- 50, 50, 100, 200
- 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.
- 90, 95, 100, 105, 100
- 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.