Exact Poisson Regression with PROC GENMOD

The script begins by creating a dataset named 'ingots' which contains the number of defective ingots ('Notready') for different combinations of heating time ('Heat') and soaking time ('Soak'), as well as the total tested ('Total'). It then calculates the logarithm of the total ('lnTotal') to use as an offset variable in the model. The PROC GENMOD procedure is then called to fit a Poisson regression model, where 'Notready' is the dependent variable. An exact conditional analysis is requested for the 'Heat' and 'Soak' parameters to obtain more precise estimates and tests, which is particularly useful with small samples.

Data Analysis

Type : CREATION_INTERNE

Data is created directly in the script using a DATA step and the 'datalines' statement.

1 Code Block

DATA STEP Data

Explanation :
This data block creates the 'ingots' table. It reads the 'Heat', 'Soak', 'Notready', and 'Total' variables from the in-line data (datalines), then calculates a new 'lnTotal' variable which is the logarithm of 'Total'. This table is the source for statistical analysis.

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1	DATA ingots;
2	INPUT Heat Soak Notready Total @code_sas_json/8_SAS_Intro_ReadFile_MultiCol_@@.json;
3	lnTotal= log(Total);
4	DATALINES;
5	7 1.0 0 10 14 1.0 0 31 27 1.0 1 56 51 1.0 3 13
6	7 1.7 0 17 14 1.7 0 43 27 1.7 4 44 51 1.7 0 1
7	7 2.2 0 7 14 2.2 2 33 27 2.2 0 21 51 2.2 0 1
8	7 2.8 0 12 14 2.8 0 31 27 2.8 1 22 51 4.0 0 1
9	7 4.0 0 9 14 4.0 0 19 27 4.0 1 16
10	;
11

2 Code Block

PROC GENMOD

Explanation :
This block uses PROC GENMOD to perform Poisson regression. 'Heat' and 'Soak' are defined as class variables. The model predicts 'Notready' based on 'Heat' and 'Soak', with 'lnTotal' as an offset variable to normalize exposure. The 'exact' statement requests an exact conditional analysis for the 'Heat' and 'Soak' variables, and 'exactoptions' sets a time limit for the status of this analysis.

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1	PROC GENMOD DATA=ingots;
2	class Heat Soak / param=ref;
3	model Notready=Heat Soak / offset=lnTotal dist=Poisson link=log;
4	exact Heat Soak / joint estimate;
5	exactoptions statustime=10;
6	RUN;

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