Date: Tue, 22 Feb 2005 14:48:51 -0800
Reply-To: Jason <falciparum@HOTMAIL.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Jason <falciparum@HOTMAIL.COM>
Subject: Re: Carry-over residuals (for a newbie)
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My interest is in accounting for the variance due to the prior
treatment; as I understand, this is called carry-over residual. For
example with the design mentioned above (where columns are people, rows
are periods, and letters are treatments):
A B C
C D B
D C A
Person 1 gets trt A, then trt C, then trt D. In the C treatment there
may be carry-over from A, and in the D treatment there may be carry
over from C. Obviously there is no carry-over for trt A because
nothing came before it (as with B for person 2, and C for person 3).
The point of assigning the first row an arbitrary category 'O' is so
they can be grouped for a variance calculation.
Let's say the response variables are the following:
22 11 13
14 11 16
21 13 14
The data in SAS might look like:
Row Col Trt Resid Response
1 1 A O 22
1 2 B O 11
1 3 C O 13
2 1 C A 14
2 2 D B 11
2 3 B C 16
3 1 D C 21
3 2 C D 13
3 3 A B 14
So no row got deleted; I wanted to be able to account for carry-over.
My question is: is this the right way to do it? Essentially I have
made Carry-over a factor in my design. So I will have reduced my MSE
degrees of freedom, but hopefully also reduced my MSE if carry-over has
an effect. Am I approaching this the right way?
>If you have random effects, why are you using PROC GLM,
>instead of PROC MIXED?
Can I get mixed to print out a nice ANOVA table like glm? Won't glm be
the same if my design is balanced and I use the RANDOM statement? (BTW
it's not the above design.)