[B.W. McCann]

Hello Everyone. 

Scenario

You apply the Q test to a data set and find that you may indeed remove a particular datum from the data set. 

Question

Why can't you apply the Q test a second time to the same data set, given that there are still plenty of degrees of freedom remaining?
 

I understand this is more of a statistics question, than a purely chemistry one.  Any and all help is appeciated.

Thank you for your attention with this question. 

Billy Wayne McCann 

[enahs]

The Q-Test is what is called a outlier test. It compares the suspected point with the total range. As you start eliminating points your range  decreases. As a results, if you repeat the process again with the new range your chances of eliminating another point increase, even if it is not an outlier of the original data set. As a result it is possible, and quite common for it to mathematically eliminate the entire data set if you repeat it. If you have two questionable points, one at the top of the range and one at the bottom, apply the q-test to both of them and see which one has the greatest confidence in throwing that one away, and discard only that one.