I am trying to determine whether there is within person change in marijuana use over time in a multilevel model with repeated measures (days nested within people).
The variables I have are:
marijuana - mj use per day
id - person id
studyday - 1-7 days
time01 - study day as 0 1 with even increments in between
Will this proc mixed code answer that question?
proc mixed data = mjuse covtest noitprint;
class id studyday;
model marijuana = time01 / solution cl outp = intp outpm = intpm ;
random intercept time01/ subject = id type = un g s gcorr;
repeated /subject=id type = ar(1);
run;
Why not:
proc mixed data = mjuse covtest noitprint;
class id studyday;
model marijuana = studyday / solution cl outp = intp outpm = intpm ;
repeated studyday /subject=id type = ar(1);
random intercept/subject=id;
run;
I guess I don't understand the coding for time01, so I automatically revert to fitting studyday.
This all assumes that marijuana is a continuous variable, and that everything has NID (0, sigma**2) errors. If your response variable is something different, or has a large skew, you may need to consider a generalized mixed model.
Steve Denham
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