Detailed Example 5 for PROC GLM (Simple Effects)

The script begins by creating a dataset named 'twoway' using datalines statements. This dataset contains three variables: A and B, which are classification variables (categorical), and Y, which is the dependent variable (quantitative). Next, the script executes PROC GLM to fit a general linear model. This model includes the main effects of variables A and B, as well as their interaction term A*B, to evaluate how the effect of one variable changes depending on the levels of the other. Finally, the LSMEANS statement is used with the SLICE=B option to examine the simple effects of variable A at each distinct level of variable B. This allows for understanding interactions by detailing the impact of A when B is held constant at a given level, and vice-versa.

Data Analysis

Type : INTERNAL_CREATION

The data used for the analysis is generated directly within the SAS script via a DATA STEP statement with datalines. The 'twoway' dataset is thus created with predefined observations.

1 Code Block

DATA STEP Data

Explanation :
This DATA STEP block creates a temporary dataset named 'twoway'. It defines three variables (A, B, and Y) and uses the DATALINES statement to populate the dataset with values specified directly in the script. The ' @code_sas/16.4'.sas at the end of the INPUT statement instructs SAS to remain on the same data line to read the next observation if available.

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1	DATA twoway;
2	INPUT A B Y @;
3	DATALINES;
4	1 1 10.6 1 1 11.0 1 1 10.6 1 1 11.3
5	1 2 -0.2 1 2 1.3 1 2 -0.2 1 2 0.2
6	1 3 0.1 1 3 0.4 1 3 -0.4 1 3 1.0
7	2 1 19.7 2 1 19.3 2 1 18.5 2 1 20.4
8	2 2 -0.2 2 2 0.5 2 2 0.8 2 2 -0.4
9	2 3 -0.9 2 3 -0.1 2 3 -0.2 2 3 -1.7
10	3 1 29.7 3 1 29.6 3 1 29.0 3 1 30.2
11	3 2 1.5 3 2 0.2 3 2 -1.5 3 2 1.3
12	3 3 0.2 3 3 0.4 3 3 -0.4 3 3 -2.2
13	;

2 Code Block

PROC GLM

Explanation :
This block executes PROC GLM on the 'twoway' dataset. The CLASS statement declares variables A and B as categorical variables. The MODEL statement specifies that the dependent variable Y is modeled as a function of the main effects of A and B, as well as their interaction A*B. 'run;' terminates this procedure step.

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1	PROC GLM DATA=twoway;
2	class A B;
3	model Y = A B A*B;
4	RUN;

3 Code Block

PROC GLM (LSMEANS statement)

Explanation :
This LSMEANS statement is a sub-statement of the previous PROC GLM. It requests the calculation of least squares means for the A*B interaction term. The SLICE=B option is crucial: it instructs SAS to analyze the simple effects of A for each level of B, which is a standard method for decomposing and interpreting a significant interaction.

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1	lsmeans A*B / slice=B;
2	RUN;

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