I'm not sure how I should set up my data for this problem which involves a longitudinal dataset with up to 20 measurements per subject.
The outcome variable is the difference between “variable Y” at time 20 and “variable Y” at time 1. My exposure of interest does not vary with time (i.e.: sex), but some of the covariates to be included in the model do change over time (i.e.: stress and time).
I have used a dataset with multiple lines per subject (one line per measurement period). In this dataset, I have created an outcome variable (change_in_Y) that represents the difference between “variable Y” at time 20 and “variable Y” at time 1. Therefore, for a given subject, the value of this variable does not change from one line to another.
This doesn’t seem right to me. How should I rearrange my dataset or outcome variable?
Here is an example of the syntax I am using:
PROC GENMOD data=A;
CLASS id ;
MODEL change_in_Y = gender stress time /dist=normal;
REPEATED sub=id/type=CS corrw;