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If the variable in question is listed in the CLASS statement, and you do not select reference (also called indicator or dummy) coding for it by specifying the PARAM=GLM or PARAM=REF option, then the default effects coding is used internally for the variable. Under effects coding, the odds ratio is not estimated by simply exponentiating a single parameter estimate. This is discussed in "Odds Ratio Estimation" in the Details section of the LOGISTIC procedure documentation.

Under effects coding, the LOGISTIC and SURVEYLOGISTIC procedures determine the appropriate contrast of parameters that defines the difference in log odds between two levels of the variable. Exponentiating this contrast's estimated value yields an estimate of the odds ratio that compares the two levels of the variable. This estimate is displayed in the Odds Ratio Estimates table.

For an illustration of how to compute odds ratios in a model that includes interaction under both indicator coding and effects coding, see Examples of Writing CONTRAST and ESTIMATE Statements. Beginning in SAS 9.2, note that odds ratios for variables involved in interaction can be estimated using the ODDSRATIO statement as illustrated in this note.

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