In reply to Rick Wicklin.

This is extremely helpful, thank you! I found the example of the predicted probability of having an underweight boy baby as a function of the mother's relative age particularly relevant to the research I'm currently doing.
I guess my 2 questions are - a) when we are evaluating an interaction as in the example (pasting code below), does it make sense to use an adjusted model? I guess since we are investigating the interaction then there is no need to adjust. b) I've been using PROC GENMOD / GEE for my model to account for clustering. To evaluate the interaction, can I use PROC LOGISTIC instead? Thank you so much! John

proc logistic data=babyWeight;
where Boy=1; /* restrict to baby boys */
model Underweight(event='1') = MomAge | CigsPerDay;
store logiModel;
run;

title "Probability of Underweight Boy Baby";
proc plm source=logiModel;
effectplot fit(x=MomAge plotby=CigsPerDay);
run;