Std Deviation, What formula does LoadRunner use?

 If you guys understand :) I am happy..if u didn't understand about the explanation .just ignore don't ask me :P

standard deviation = square root of variance

variance is  calculated from the below formula

σ2 =  E(X-M)^2

--------

N-1

where M is the mean (which is nothing but avg ) of all the values and N is the total number.

* here E has to be in the symbol of summation .(as our computer doen't support the symbol i am

unable to provide you with the actual one ).

Loadruner also utilises the same formaula .

but in our analysis we can see only max, avg, min values.

but the graph provides you with almost all the values

at diffenet times.

So first claculate the mean and find the variance and the square root of variance gives you the standard deviation.

for example;-for the numbers 1,2 and 3 the mean is 2 and the variance is .667

mean = M = 1+2+3

----- = 2

3

Variance = (1-2)^2+(2-2)^2+(3-2)^2

----------------------- = 0.667

3

standard deviation = 0.816