# What is your standard deviation?

I'm just wondering what is a normal or what is a good number I had not heard of this until I downloaded my cgm and saw my SD number so I went on to google it to see what I could find, but I figured I get better answers here, so I wonder if anyone keeps track of that and if there is a number we should try to aim for and keep it at?

27 when I checked earlier in the week.

Only during the last year have I begun to appreciate the value of monitoring standard deviation. I think it's more important than A1c as an indication of good BG control. Standard deviation reflects BG variability, something the A1c doesn't reflect at all.

Any standard deviation number should also include the period covered. My standard deviation for the last seven days is 35. Last week it was 42. During the last month it was 41 and the last 90 days it was 49. My goal is a standard deviation for all periods at 30 or under.

A standard deviation of 30 means that 68% of BG numbers fall within +/- 30 of the average. If the average is 110, then 68% of the BG numbers fall within 80-140.

I'm working on a better standard deviation and it is improving.

You're line of questioning is worthwhile. Good luck!

I apologize if I answered with more than you asked but I thought that other readers would appreciate some context.

I think this is a really good question. From my experience, endos don't pay nearly enough attention to the SD and I think there is just beginning to be some understanding that a lower SD (even in the presence of a slightly higher A1C) is healthier in the long run. From what I understand, higher SDs are thought to increase the chances of developing complications.

My current SD is 52 for the last two weeks (just checked my data). I need to work on getting that down....

Good Q. I recently just read somewhere that a starting point for a goal can be: try to get it less than half of your target BG. For example if your target BG is 90, then try to get a Standard Deviation of 45 or less.

It's true that the SD number should be viewed considering the period of days over which it has been measured. I just summarized mine for my next trip to the blood (witch?) doctor and I got 48 (over the last 3 months) and 42 (over the last 3 weeks.)
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I used to plot a frequency chart of my BG readings it gave a preaty good normal curve with average and SD clearly visible. The Endo did not even look at it he was an A1c man only. I guess he did not like the inaccuracy of the new 5 second meters but was unwilling to lobby the Govt for more accuracy requirements. Inconsistent.

awesome info thanks for sharing! :)

I guess it's only fair to share my SD # according to my Dexcom from April 30th to July29th it was 80. Now it says from Oct29-Jan28 its 60 so it has gone done significantly right?

wow that's a great SD # so your BS must be less than 120 most of the time?

My endo is an A1c man, too. While he prescribed my CGM, he's uninterested in any statistical analysis to guide clinical recommendations. After I was on the CGM for awhile, I brought my netbook computer to the endo appointment to show him all the graphs and pie charts.

His interest was zero as he continued to rifle through his paper file of my records with an eye toward finishing his agenda before the 15 minute visit expired.

I have a hard time respecting this standard of care!

well, 27 would just mean it doesn't go too far from the average very much but yeah, I try to keep my average pretty tightly controlled?

so how do I go about knowing my SD# without my dex, if I want a SD# for one week do I add up all my numbers and then figure out the mean or do I have to do something else?

One thing that I've learned, the things that you pay attention to (measure and monitor) often improve simply because you're watching them!

Keep up the good work; you're headed in the right direction.

I've noticed lately that on days where my SD is in the 20s, I have more energy and my disposition brightens.

This wikipedia page explains well how standard deviation is calculated. It's not too complicated.

You could take the numbers from your finger-stick meter (from whatever period of time you choose) and calculate the standard deviation. Alternately, spreadsheet programs like Excel contain the formulas for calculating SD.

Your curiosity hints at good success with the evil D!

awesome thanks so much for all the info!! and you have no idea how hard I'm trying to bring my numbers down I have gone from no exercise to exercising 6x's a week eating out 3 to 4x's a week to limiting it down to twice a week if that. My fasting glucose use to be 200-240 now its 100-160, after meals it used to go way over 250 now its rare if it goes over 220 still have a lot of work to do but I'm getting there :)

Congrats, you're doing all the right stuff. Now the hard part -- sustain!

I don't get an endo who is only interested in your A1C? I like A1C just fine but it's a "strategic" number and you don't win a war without the "tactical" successes of the little battle that each BG test represents?

RE calculating it without a Dexcom (my MiniMed does it too...) or doing any math, I had a One Touch Ultra Smart meter that calculated SD a few years ago. I think it might have "displayed" it without downloading it. Unfortunately, I dropped it on my bike and it's long gone...

I find the SD useful as a measure of how closely I have managed my blood sugar and in particular, how much I have kept my after meal (and exercise) numbers well controlled. I think for many of us, the SD is not critical. But when you start to push for "tight" control it matters a great deal. The most accurate estimates of SD come from a CGMS, but you can get reasonable estimates from just testing (which is what I do).

At least in my case, my SD helps me predict how "safe" I am. It tells me how likely I am to avoid lows. 95% of my readings will be within two standard deviations of my blood sugar average. If I want to lower my average blood sugar (and hence my A1c), I need to tight up my SD or I will have lows.

If your A1c is say 7%, then a good way of estimating your target SD is to figure that an A1c of 7% corresponds to an average blood sugar of 154 mg/dl. If you want to have 95% confidence that your blood sugar readings won't go below 60 mg/dl, then you want your SD to be (154-60)/2 = 47. If you tighten things up and want an A1c of 5.5% and don't want to go below 60 mg/dl, then you need an SD of 25.

ps. And I apologize for the math

LOL, no apologies necessary! I like the explanations of the math items to fill in the considerable "fuzziness" since I'm such a lazyass about it, just looking at my gizmo to tell me the result?