Example 28.4 Log-Linear Model, Three Dependent Variables

This analysis reproduces the predicted cell frequencies for Bartlett’s data by using a log-linear model of no three-variable interaction (Bishop, Fienberg, and Holland; 1975, p. 89). Cuttings of two different lengths (Length=short or long) are planted at one of two time points (Time=now or spring), and their survival status (Status=dead or alive) is recorded.

As in the text, the variable levels are simply labeled 1 and 2. The following statements produce Output 28.4.1 through Output 28.4.3:

   data bartlett;
      input Length Time Status wt @@;
      datalines;
   1 1 1 156     1 1 2  84     1 2 1 84     1 2 2 156
   2 1 1 107     2 1 2 133     2 2 1 31     2 2 2 209
   ;

   title 'Bartlett''s Data';
   proc catmod data=bartlett;
      weight wt;
      model Length*Time*Status=_response_ 
            / noparm pred=freq;
      loglin Length|Time|Status @ 2;
      title2 'Model with No 3-Variable Interaction';
   quit;