|The GENMOD Procedure|
If you define a link function in the FWDLINK statement, then you must define the inverse link function by using the INVLINK statement. If you use the MODEL statement option LINK= to specify a link function, you do not need to use the INVLINK statement. The variable identifies the inverse link function to the procedure. The expression can be any arithmetic expression supported by the DATA step language, and it is used to define the functional dependence on the linear predictor.
Alternatively, the inverse link function can be defined using programming statements (see the section Programming Statements) and assigned to a variable, which is then listed as the expression. The second form is convenient for using complex statements such as IF-THEN/ELSE clauses. The automatic variable _XBETA_ represents the linear predictor in the preceding expression.