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Re: st: repeated factor ANOVA
From
James prince <[email protected]>
To
[email protected]
Subject
Re: st: repeated factor ANOVA
Date
Tue, 2 Oct 2012 14:38:02 -0500
Thank you Phil. Just what I need it.
The reason for the ANOVA is to compared results to a previous analysis
of these data using SAS.
They used PROC MIXED with option REPEAT.
When I used XTMIXED, I could not match their results.
I now match their results with Stata's ANOVA
Thank you again,
Jim
On Tue, Oct 2, 2012 at 9:57 AM, Philip Ender <[email protected]> wrote:
> On 10/2/2012 James prince <[email protected]> wrote:
>
> Hello,
>
> I am unsure how to set-up the following problem using the ANOVA
> command. Any help would be appreciated.
>
> I have data on 600 liver patients, 300 assigned to one of two
> treatment groups (TREAT).
> Each had 4 biopsy (one in each quadrant: UR, UL, LR, LL) and the
> concentration on an enzyme (Y) measured. I also have data for sex. I
> know that I can used XTMIXED to do this, but I need to use ANOVA
>
> Thank you in advance,
> Jim
>
> --------------------------------------------------------------------------------------
>
> This is what I did: I first tried using a repeated ANOVA but got an error:
>
> . anova y treat liver sex subj, repeat(subj)
> could not determine between-subject error term; use bse() option
>
> Then,
> If I set it up as nested, I get a result, but I am not sure if it is correct.
> anova y treat liver sex/ subj|liver/ ...
>
> You say you need to use -anova- but you don't say why you need to use
> -anova-. For balanced designs -xtmixed- and -anova- yield equivalent
> results although somewhat differnt p-values due to chi-square vs
> F-ratio. If the design is unbalance within subject then -xtmixed- is
> much better. With your large sample size the p-value issue should be
> moot.
>
> All that aside, here is the -anova- code to run your analysis without
> sex. The error term for treat is subj|treat. There should be a treat
> by liver interaction and the repeated factor is liver.
>
> anova y treat / subj|treat liver treat#liver /, repeat(liver)
>
> If you want to include sex you need to treat it as a between subject
> factor. The error term for the between subject factors is
> subj|treat#sex. You also get more interactions
>
> anova y treat sex treat#sex / subj|treat#sex liver sex#liver
> treat#liver sex#treat#liver /, repeat(liver)
>
> -xtmixed- code is much simpler:
>
> xtmixed y treat##sex##liver || subj:, reml var
>
>
> --
> Phil Ender
> UCLA Statistical Consulting Group
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