Is it possible to stratify when you only have two levels? For instance, my outcome is sleep duration, while my exposure is read to. I am trying to determine if the third variable ADHD severity would modify the relationship between sleep duration and read to. All three are categorical variables. See below
Sleep Duration(1= Meet requirement, 2= do not meet)
Read to (1= 0-3 days, 2= 4-6 days, and 3= Every day)
ADHD Severity( 1= Mild and 2= Moderate/Severe)
My question is, is it possible to stratify based on ADHD severity. I think it is not possible since one of the levels of ADHD severity has to be a reference group. My current analysis did not stratify based on the level of ADHD severity (See attached SAS output). I need clarification and if possible what is the appropriate SAS code. Thanks.
