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.

  • $\begingroup$ "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 ... $\endgroup$
    – user1551
    Dec 17, 2012 at 10:38
  • 1
    $\begingroup$ 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. $\endgroup$
    – rro
    Dec 17, 2012 at 10:53
  • 3
    $\begingroup$ 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. $\endgroup$ Dec 17, 2012 at 11:00

2 Answers 2


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"



  • $\begingroup$ Could you please share your source of information for this? $\endgroup$
    – rro
    Dec 20, 2012 at 1:59
  • $\begingroup$ I have listed a couple of references above. $\endgroup$ Dec 20, 2012 at 17:00
  • $\begingroup$ It seems dubious to me to extend this outside of the financial industry (if that's where its used). Logically the CV can only be greater than 1 if the Std deviation is higher than the mean. Which in most data sets seems unlikely. $\endgroup$
    – Morvael
    Nov 9, 2020 at 11:36

When trying to figure this out myself I opted for using the Std deviation as a percentage of the range. Looking at this graph:

enter image description here

from that image I would I would say that the SD of 5 was clustered, and the SD of 20 was definitionally not, the SD of 10 is borderline.

More mathematically,

  • The SD of 5 has 68% of the values within 10% of the range
  • The SD of 10 has 68% of the values within 20% of the range
  • The SD of 20 has 68% of the values within 40% of the range

So as a purely internal measure of High / Low Std deviation I chose to say if the SD was less than 10% of the range then its low, greater than 10% of the range then high.

But you could of course choose different percentages based on your own data sets.



You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .