Obsidian | Level 7

## How do I do slice test for effects when interaction is significant in 2 X 2 factorial

Dear SIr,

I had tried to analyse a 2 X2 factor experiment with PROC GLM. I reported the P-values for A, B and AB interaction.

My SAS syntax was of this fashion:

proc univariate plot normal;
title 'Trial4Digest';
var v1;
run;
Proc GLM Order = Data;
Class A B;
Model v1 = block A B A*B;
LSmeans A*B/TDIFF PDIFF P STDERR Adjust=tukey;
Run;
Quit;

1. Where interaction was NOT SIGNIFICANT, I had used the simple effect of each factor to compare my means and report in result and discussion.

2. Where interaction was SIGNIFICANT and either FActor A or B is Sig, or FActor A or B is NOT SIGNIFICANT, i had used tukey test to assign "abcd" to the means for comparisons.

 A1 A2 P-values 3Parameter B- B+ B- B+ SEM A B A*B Ac 58.4 51.5 54.2 55.7 0.71 0.86 0.02 ˂0.01 Pro 20.5b 23.3a 22.5a 23.2a 0.39 0.07 <0.01 0.05 Bu 15.5 18.8 17.5 15.8 0.37 0.40 0.19 ˂0.01 Bra 3.66 3.96 3.80 3.30 0.10 0.19 0.54 0.04 Val 1.95b 2.39a 1.98b 2.00b 0.06 0.02 <0.01 0.01 Ap 3.03a 2.25b 2.46b 2.43b 0.09 0.175 0.01 0.01

This is the response of the reviewer:

" The use of Tukey's test to separate means is incorrect. Actually, it is not acceptable to use two statistical tests to show a difference between treatments (treatments and interaction effects and mean separation). I greatly discourage the authors from using mean separation when the effect of treatment (factor A, factor B and interaction) is displayed in the tables. A slice test can be used when the interaction is observed. Therefore Tables and text (where appropriate) should be corrected".

I do not have a clue on the way forward on using this slice test and how to interpret the subsequent result. Any help to modify my syntax and report correctly will be appreciated.

Thank you

Rhodochrosite | Level 12

## Re: How do I do slice test for effects when interaction is significant in 2 X 2 factorial

You can obtain comparisons of simple effects using the SLICE statement that is available in several procedures, including MIXED and GLIMMIX but not GLM, see the SLICE Statement documentation

or you can use the SLICE option on the LSMEANS or LSMESTIMATE statement in the MIXED and GLIMMIX procedures.

I hope this helps.

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