Example 4 for PROC CATMOD: Log-Linear Model

This SAS^© script implements a log-linear model to analyze Bartlett's data, which examines the survival status (dead or alive) of cuttings of different lengths, planted at two distinct times. The model explores the interactions between cutting length, planting time, and survival status, excluding the three-variable interaction. The CATMOD procedure is used for this analysis.

Data Analysis

Type : CREATION_INTERNE

Bartlett's data is created directly in the script via a DATALINES block. The variables are 'Length' (long/short), 'Time' (spring/immediately), 'Status' (dead/alive) and 'wt' (weight/frequency).

1 Code Block

DATA STEP Data

Explanation :
This DATA Step block creates the 'bartlett' dataset from internal data provided via the DATALINES statement. It defines the variables Length, Time, Status, and wt, representing respectively the cutting length, planting time, survival status, and the weight or frequency of each factor combination. The invalid part of the INPUT line (` @code_sas_json/8_SAS_Intro_ReadFile_MultiCol_@@.json`) has been removed to make the code executable.

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1	DATA bartlett;
2	INPUT LENGTH Time STATUS wt;
3	DATALINES;
4	1 1 1 156
5	1 1 2 84
6	1 2 1 84
7	1 2 2 156
8	2 1 1 107
9	2 1 2 133
10	2 2 1 31
11	2 2 2 209
12	;
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2 Code Block

PROC CATMOD

Explanation :
This block uses PROC CATMOD to fit a log-linear model to Bartlett's data. The `weight wt` option indicates that the 'wt' variable contains the observation frequencies. The `model` statement specifies the model variables and `_response_` indicates that the model applies to the implicit response variable. The `noparm` and `pred=freq` options are used for output. The `loglin` statement fits a log-linear model without a third-order interaction (specified by ` @ 2`), exploring interactions up to order 2 between Length, Time, and Status.

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1	title 'Bartlett''s Data';
2	PROC CATMOD DATA=bartlett;
3	weight wt;
4	model LENGTHTimeSTATUS=_response_
5	/ noparm pred=freq;
6	loglin LENGTH\|Time\|STATUS @ 2;
7	title2 'Model with No 3-Variable Interaction';
8	QUIT;
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