The Fisher's LSD, Duncan's, Newman-Keuls, and Tukey HSD procedures all use the same formula for computing t . They differ in the critical value. The 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.