Computes individual pairwise comparisons using Student’s t-tests. If you make many pairwise tests, there is no protection across the inferences. Therefore, the alpha-size (Type I error rate) across the hypothesis tests is higher than that for individual tests. See Each Pair, Student’s t.
Shows a test that is sized for all differences among the means. This is the Tukey or Tukey-Kramer HSD (honestly significant difference) test. (Tukey 1953, Kramer 1956). This test is an exact alpha-level test if the sample sizes are the same, and conservative if the sample sizes are different (Hayter 1984). See All Pairs, Tukey HSD.
Note: If you have specified a Block column, then the multiple comparison methods are performed on data that has been adjusted for the Block means.
Related Information 

Help created on 9/19/2017