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Very many, these are tests that allow to identify the samples that differ among the X that we tested beforehand.

Introduction

Post-Hoc, or posterior, tests allow to identify among X groups which group differs, the Hypothesis Testing Having slept and already indicated that there was a difference.

This is typical of clinical trials: We have many different groups and our challenge is to determine which group is different.

You can use multiple tests based on the level of complexity of our problem and the previous text:

  • If you want to compare all the averages 2 to 2, you can use the HSD Test of Tukey.
  • If we want to compare groups in personalized ways (1 group with 1 control group, 2 groups with 3 other groups…), we will use the Scheffé test.
  • We did an ANOVA and we want to know which groups are different. The list below presents the tests that can be done from the most lax to the most conservative.

Name of the post HOC test

Comment

Fisher’s Least significant difference (LSD) – test of the smallest difference

To be used for a comparison of 3 samples

Student Newman-Keuls PPAS-smaller significant amplitude

For 3 to 5 samples maximum, because the error level increases almost linearly with the number of pairs of samples to be tested.

Tukey Honestly significant difference (HSD) – Really significant difference Test

Very conservative, it will allow to calculate the probability of error at the level of risk chosen. Attention, it can only be used if the data is normal.

The procedure REGW test Q and F-Ryan-Einot-Gabriel-Welsch

This test requires the use of software because the calculation requires automation.

Duncan new multiple range test (MRT)

Derived from the Newman-Keuls test, this test is more protective against the second species error with the consequence of having a greater risk of first species.

Dunnett

This test is used when you want to compare 1 sample with all the others.

The Bonferroni procedure (Bonferonni correction)

Probably the most used but it lacks power.

Holm Bonferroni

More powerful than the Bonferroni procedure, this method provides a correction that allows to be more restrictive and to detect weaker deviations.

Scheffé

Derived from Student’s T, ultra Conservative, it will be used for complex comparisons.

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