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I have derived the following response time data for a performance test I am running:

Min - 8sec Max - 284sec Average - 28sec Standard Deviation - 27sec

What does the standard deviation say about the response time data distribution? When you say low/high standard deviation, what does this actually mean? Is this in comparison to the Average/Min/Max?

I know what standard deviation is and how it's computed. I'm just not sure how to tell if it is high or low.

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"I know what standard deviation is". Hmm ... if you do know what standard deviation is, you should know that it is a measure of dispersion of data ... –  user1551 Dec 17 '12 at 10:38
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Yes, what confuses me is how to tell if a standard deviation is high or low. The examples I've read so far have not said what makes it high or low. –  raymond Dec 17 '12 at 10:53
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Aren't terms like "high" or "low" just a matter of subjective judgement? The data you have seem to suggest that time is very roughly speaking 28sec +/- 27 sec, so in a very naive sense you expect the results to usually fall between 1sec and 60sec. I'd say it's rather high deviation, but I suppose it depends on the characteristic of a problem. –  Feanor Dec 17 '12 at 11:00
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1 Answer

up vote 5 down vote accepted

If you take your cues from the financial industry, you can use the coefficient of variation (CV), which is the standard deviation / mean. This formula is used to normalize the standard deviation so that it can be compared across various mean scales.

As a rule of thumb, a CV >= 1 indicates a relatively high variation, while a CV < 1 can be considered low.

Some references to usage as "rule of thumb"

http://www.readyratios.com/reference/analysis/coefficient_of_variation.html

http://www.mhnocc.org/forum/index.php?t=msg&goto=234&

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Could you please share your source of information for this? –  raymond Dec 20 '12 at 1:59
    
I have listed a couple of references above. –  Ralph Winters Dec 20 '12 at 17:00
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