Performs all pairwise comparisons between group means, testing for
significance using Scheffe's F-test. Returns an upper-triangular table in a
format described in the manual. Also see the function
print-scheffe-table.'<br> <br> Group-means' and
group-sizes' should be sequences. The arguments ms-error'
and `df-error' are the mean square error within groups and its degrees of
freedom, both of which are computed by the analysis of variance. An ANOVA test
should always be run first, to see if there are any significant differences.