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The GENMOD Procedure 
The data set and SAS statements that fit the model by the GEE method are as follows:
data six; input case city$ @; do i=1 to 4; input age smoke wheeze @@; output; end; datalines; 1 portage 9 0 1 10 0 1 11 0 1 12 0 0 2 kingston 9 1 1 10 2 1 11 2 0 12 2 0 3 kingston 9 0 1 10 0 0 11 1 0 12 1 0 4 portage 9 0 0 10 0 1 11 0 1 12 1 0 5 kingston 9 0 0 10 1 0 11 1 0 12 1 0 6 portage 9 0 0 10 1 0 11 1 0 12 1 0 7 kingston 9 1 0 10 1 0 11 0 0 12 0 0 8 portage 9 1 0 10 1 0 11 1 0 12 2 0 9 portage 9 2 1 10 2 0 11 1 0 12 1 0 10 kingston 9 0 0 10 0 0 11 0 0 12 1 0 11 kingston 9 1 1 10 0 0 11 0 1 12 0 1 12 portage 9 1 0 10 0 0 11 0 0 12 0 0 13 kingston 9 1 0 10 0 1 11 1 1 12 1 1 14 portage 9 1 0 10 2 0 11 1 0 12 2 1 15 kingston 9 1 0 10 1 0 11 1 0 12 2 1 16 portage 9 1 1 10 1 1 11 2 0 12 1 0 ; proc genmod data=six ; class case city ; model wheeze = city age smoke / dist=bin; repeated subject=case / type=exch covb corrw; run;
The CLASS statement and the MODEL statement specify the model for the mean of the wheeze variable response as a logistic regression with city, age, and smoke as independent variables, just as for an ordinary logistic regression.
The REPEATED statement invokes the GEE method, specifies the correlation structure, and controls the displayed output from the GEE model. The option SUBJECT=CASE specifies that individual subjects are identified in the input data set by the variable case. The SUBJECT= variable case must be listed in the CLASS statement. Measurements on individual subjects at ages 9, 10, 11, and 12 are in the proper order in the data set, so the WITHINSUBJECT= option is not required. The TYPE=EXCH option specifies an exchangeable working correlation structure, the COVB option specifies that the parameter estimate covariance matrix be displayed, and the CORRW option specifies that the final working correlation be displayed.
Initial parameter estimates for iterative fitting of the GEE model are computed as in an ordinary generalized linear model, as described previously. Results of the initial model fit displayed as part of the generated output are not shown here. Statistics for the initial model fit such as parameter estimates, standard errors, deviances, and Pearson chisquares do not apply to the GEE model, and are only valid for the initial model fit. The following tables display information that applies to the GEE model fit.
Figure 29.7 displays general information about the GEE model fit.
Figure 29.8 displays the parameter estimate covariance matrices specified by the COVB option. Both modelbased and empirical covariances are produced.

The exchangeable working correlation matrix specified by the CORRW option is displayed in Figure 29.9.

The parameter estimates table, displayed in Figure 29.10, contains parameter estimates, standard errors, confidence intervals, Z scores, and pvalues for the parameter estimates. Empirical standard error estimates are used in this table. A table using modelbased standard errors can be created by using the REPEATED statement option MODELSE.

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