Thread: Let's talk about velocity Extreme Spread (ES)

Now to take it further, let's say you have to choose between load 2 and load 3 with 95% confidence. To compare two SD's you perform an F-Test (in excel).

First calculate the variance of the two samples e.g. var(a1:a10).
Now divide load 2's variance by load 3's variance. 68.7/291.6 = 0.24. This is the F-statistic.
Now get the alpha value. 1-0.95 = 0.05.

Now to check if load 2 is better than load 3: f.inv(alpha, load 2 samples -1, load 3 samples -1) e.g f.inv(0.05, 9, 9) = 0.31 F-critical left.
Because the F-statistic is less than the F-critical left (0.24<0.31), we can say with 95% certainty that load 2 is better than load 3.

Now to check if load 2 is worse than load 3: f.inv.rt(0.05, 9, 9) = 3.18 F-critical right.
Because the F-statistic is less than the F-critical right (0.24<3.18), we cannot say load 2 is worse.

Hopefully I explained this simply enough. I've attached the example excel file.
F-Test.xls