All Pairwise Comparisons among Means: Recapitulation and Recommendations
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The Fisher's LSD,
and Tukey HSD
all use the same formula for computing t .
They differ in the critical value.
following figure shows the critical values for an experiment with 10
treatment conditions and four subjects per condition as a function of
the number of means spanned in the comparison.
Note that the number of means spanned does not affect the critical
value for either Tukey's HSD or Fisher's LSD. The former uses the
most conservative (highest) critical value for all comparisons
whereas the latter uses the least conservative (lowest) critical
value for all comparisons. The Newman-Keuls and the Duncan procedures
increase the critical value as a function of span, although Duncan's
does not increase it much.