Logistic Regression – Quick Tips

When doing Logistic regression in SAS there are several procedures that you can use:

  • Proc Logistic
  • Proc Genmod
  • Proc Surveylogistic
  1. If you’re using survey weights then you need to use SurveyLogistic to have your variance and confidence intervals calculated appropriately.
  2. For categorical variables, use a CLASS statement and specify PARAM=REF to use referential coding. If you use EFFECT coding (the default option) then your p-values may not align with your odds ratio confidence intervals.
  3. Use the ODDSRATIO statement to get odds ratio for specific variables or to compare different levels.
  4. /EXPB after your model statement will allow you to have the ratios included in your output.
  5. Check the event selection that is modelled in SAS. By default SAS models the event Y=0, when you usually want Y=1. You can modify by specifying the event in your model statement.

So that are some quick heads up regarding using proc logistic in SAS.

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