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Standard deviation

lely

Well-Known Member
Messages
208
Hi all. I'm using the accu-check expert, and in trying to understand all features I'd like to know, what standard deviation is.
I've googled it but am still a bit confused as to its meaning in relation to Bg results.
Is it the variation of the results above or below the average.
So if the average is 11.2 and the SD is 4. Does that mean it as high as 15 and as low as 7.
Or I'm I completely on the wrong track.
I swear this would be easier if you were young and still doing maths every day. :-?
 
standard deviation
noun
STATISTICS
  1. a quantity expressing by how much the members of a group differ from the mean value for the group.
    1. The standard deviation is kind of the "mean of the mean," and often can help you find the story behind the data. To understand this concept, it can help to learn about what statisticians call "normal distribution" of data.
    2. Standard Deviation - Robert Niles
      www.robertniles.com/stats/stdev.shtm
Do these help ?

RRB
 
Hi RRB, yes more clear now.
If the average is 11 and deviation is, say 2. Most readings are around this if it's say 4 the results are more varied around the average.
I'll need to read it over again before it completely sinks in.
But the results make more sense now and I see I need to make a better effort. :-o
 
The SD is the measure of how dispersed the values are from the mean, so with a SD of 2 the values are more tightly grouped round the mean than if the SD were 4.
In the example the values may, or may not be as high or low as 7 or 15 exactly

sd = SQRT(SumOf(Value-mean))
 
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@lely

if you have the book Think Like a Pancreas look-up SD, the following is from an article on the net where Gary briefly explains what SD is all about:

''The standard deviation (SD) reflects the amount
of variability in your readings. Lower is better.
If the SD is more than half of your average, your
readings include many extreme highs and/or
lows. A SD that is less than one third of your
average means that your readings are fairly
consistent from day to day, without too many in
the extreme ranges.''
 
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@lely - I find SDfromMean one of the most important pieces of information in judging how well I am managing my BG. As soon as the SDfromMean starts increasing, you know your control is slipping regardless of what your HbA1c might be telling you. I wish the medical profession would use this measure as an indication of control far more than they do.

The three measures Dr. Bernstein tells us to use to assess our control are:

1. Average
2. SDfromMean
3. Percentage of readings in target.

All three together show the effectiveness of management of BG.

Smidge
 
Standard Deviation is a way of measuring variance. It's not the min or max values, just simply a standard way of measuring variance in a sample of numbers. To put a number on it, it means that 66% of your BG numbers are within the SD range. So, yes, you are correct when you say it means average +/- SD.

If your SD is small, it means your numbers are steady, if large your numbers will be all over the place.
 
For a normal distribution, empirically 68% of all results will be within one standard deviation of the mean (pretty much what Sam just said). 95% of results will be within 2 standard deviations, and 99.7% within 3.
 
@smidge
Yes I've been using the percentage of readings on target, which since November has been gradually increasing however now I look at the SD they are all around 3-4 which I see is probably not great and needs improvement

@CarbRok
That looks a little complicated for a Sunday evening, I'll read that tomorrow when kids are at school.
Thank you all once again for the most valuable info.
 
I try to keep my SD somewhere between 2.1 and 2.8 over 90 day average with my Roche gadgetery.

I believe that this has eliminated my background retinopathy which I
did have 5 years ago.

I try to keep my 90 day average at 6.5ish...

Roche tend to have higher 90 day readings than your hba1c which is why I try to keep to 6.5. I just chose the number from the airbreally but based on using their gadgets for years....

I peesonally firmly believe the larger the SD the more complications.. But thats only my opinion and there is no proof of this as far as I lnow.

However this is all depending on the amount of blood tests you actually do a day. My average is 10 including nightime testing. If it was one, then it would mean ****** all!!
 
Which is why having things like the libre working properly would be a huge advantage.
 
I rarely look at the report menu on the Expert or the Combo when I used the pump.
 
lely said:
@smidge
Yes I've been using the percentage of readings on target, which since November has been gradually increasing however now I look at the SD they are all around 3-4 which I see is probably not great and needs improvement
Click to expand...


Again, referring to the book Scheiner says a SD of around 2 means good bg control.
 
Always wondered what standard deviation was about - my SD for the last 30 days was 1.4, last week was 1.1


 
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