10.8. GENMOD versus CATMOD

I’ve used PROC GENMOD exclusively in this chapter, but you can also estimate loglinear models with PROC CATMOD. I prefer GENMOD for three reasons:

  • PROC GENMOD uses a dummy variable parameterization for CLASS variables while PROC CATMOD uses “effect coding.” As I explained in Section 5.8, I find PROC CATMOD’s parameterization difficult to interpret.

  • PROC GENMOD can fit a wider range of loglinear models than PROC CATMOD. Most importantly, PROC CATMOD does not allow the device of treating a variable as both quantitative and qualitative in the same model.

  • PROC GENMOD can correct for overdispersion when appropriate.

  • PROC GENMOD can optionally produce likelihood-ratio hypothesis tests.

    PROC CATMOD only produces Wald tests.

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