computes the deviate, , associated with the lower tail probability of the distribution of the Studentized range statistic.
The externally Studentized range,, for a sample, is defined as:
Where is an independent estimate of the standard error of the 's.
For a Studentized range statistic the probability integral, , for degrees of freedom and groups, can be written as:
For a given probability , the deviate is found as the solution to the equation