I've just upgraded from SAS v9.1 to v9.2, and noticed the nice addition of AIC and other information criteria in the GENMOD procedure Goodness-of-fit output. However, I also noticed that the Deviance and Pearson Chi-square are not printed by default, but must be requested by the AGGREGATE option to the MODEL statement.
The trouble is, for some reason that I don't quite understand, that when I leave the AGGREGATE option out, the Full Log Likelihood statistic becomes equal to the Log Likelihood, but when I give the AGGREGATE option the Full Log Likelihood statistic changes -- and consequently the AIC which is calculated from this (identical output in all other respects).
As an example, the Goodness-of-fit output from two identical models (dist=bin,link=logit), save for the aggregate option. Note in particular the change in Full Log Likelihood.
Without AGGREGATE option:
Criterion DF Value Value/DF
Log Likelihood -383.3357
Full Log Likelihood -383.3357
AIC (smaller is better) 770.6714
AICC (smaller is better) 770.6818
BIC (smaller is better) 780.7907
With AGGREGATE option:
Criterion DF Value Value/DF
Deviance 1082 722.9896 0.6682
Scaled Deviance 1082 722.9896 0.6682
Pearson Chi-Square 1082 1067.9233 0.9870
Scaled Pearson X2 1082 1067.9233 0.9870
Log Likelihood -383.3357
Full Log Likelihood -372.1276
AIC (smaller is better) 748.2552
AICC (smaller is better) 748.2655
BIC (smaller is better) 758.3744
All other output is identical. Should these values not be the same?