Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: st: repeated factor ANOVA
From
Philip Ender <[email protected]>
To
[email protected]
Subject
Re: st: repeated factor ANOVA
Date
Tue, 2 Oct 2012 07:57:52 -0700
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
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/faqs/resources/statalist-faq/
* http://www.ats.ucla.edu/stat/stata/