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Walid and everyone,
This got more interesting when I started working with a full simulated dataset. The first thing is that your data has replicate completely confounded with animal. I don't think this is the case--so I recoded replicate as 1, 2, 3 for each animal. It then becomes a lot more apparent that there is a lot of nested random effects: pen, animal within pen, replicate within animal for each week. I also ginned up a second day's worth of data
The following code "works". I still feel like there might be something better.
proc mixed data=sasl;
class pen TRT Day animal replicate;
model response= TRT Day TRT*Day ;
random pen animal(pen) replicate(animal pen);
repeated Day / subject = animal(pen) type = cs r rcorr;
lsmeans TRT Day TRT*Day/diff;
run;
Notes: Take a look at that r matrix. It has six entries--3 reps by 2 days. There has to be something better. A group statement perhaps?
Steve Denham
Associate Director, Biostatistics
MPI Research
----- Original Message ----
From: Walid Alali <walidalali@GMAIL.COM>
To: SAS-L@LISTSERV.UGA.EDU
Sent: Wednesday, March 26, 2008 3:16:13 PM
Subject: Repeated measure in Mixed procedure
Hello all,
I am having trouble finding the best way of including all sources of
variability in my mixed model.
My study design (which is a clinical trial) goes like this: I have 3 pens,
in each pen; 10 animals (5 exposed and 5 controls). The response (i.e.
the outcome) is measured over time (every week for 2 months). To make this
complicated, the response was measured in triplicate (i.e. 3 times) at
each time point.
Here is a glimpse of the data (just for the 1st pen):
Animal TRT DAY Pen Replicate response
151 E 0 5 1 6.75E+03
151 E 0 5 1 6.22E+03
151 E 0 5 1 4.98E+03
152 E 0 5 10 6.25E+03
152 E 0 5 10 8.92E+03
152 E 0 5 10 6.09E+03
153 E 0 5 2 7.38E+03
153 E 0 5 2 4.68E+03
153 E 0 5 2 6.94E+03
154 E 0 5 3 2.49E+03
154 E 0 5 3 2.31E+03
154 E 0 5 3 2.03E+03
155 E 0 5 4 1.32E+04
155 E 0 5 4 9.92E+03
155 E 0 5 4 9.49E+03
156 C 0 5 5 4.22E+03
156 C 0 5 5 4.21E+03
156 C 0 5 5 3.46E+03
157 C 0 5 6 3.70E+03
157 C 0 5 6 3.62E+03
157 C 0 5 6 2.85E+03
158 C 0 5 7 1.54E+03
158 C 0 5 7 1.38E+03
158 C 0 5 7 1.63E+03
159 C 0 5 8 5.16E+03
159 C 0 5 8 5.00E+03
159 C 0 5 8 4.66E+03
160 C 0 5 9 5.37E+03
160 C 0 5 9 5.30E+03
160 C 0 5 9 5.41E+03
I have the model set up like this, but not sure how to include 'replicate'
in it??
proc mixed data=data;
class pen TRT Day animal;
model response= TRT Day TRT*Day ;
random pen;
repeated Day / subject = animal(TRT) type = un r rcorr;
lsmeans TRTcode Day TRTcode*Day/diff;
run;
Any comments, suggestions are very wellcome.
Thanks in advance,
Walid.
Walid Alali DVM, MS, PhD
Epidemiology
Post-doctoral Research Associate
Department of Veterinary Integrative Biosciences
College of Veterinary Medicine and Biomedical Sciences
Texas A&M University
4458 TAMU
College Station, TX, USA 77843-4458
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