Re: st: RE: Covariates in ANOVAs

[David Airey <david.airey@vanderbilt.edu>]

.

xi3 is not recommended for the following commands:

"Note: xi3 is not compatible with the following Stata commands:  
xtmixed, xtmelogit or xtmepoisson."

Furthermore, ATS UCLS is no longer supporting this command, and passed  
off to -desmat-.

If Stata would just expand xi's capabilities, we could be happier.

-Dave


On May 14, 2009, at 10:48 PM, Joseph Coveney wrote:

> Miss Gina Micke wrote:
>
> I would like to know how to control for an independent continuous  
> variable when
> using a repeated measures ANOVA. I have a 2x2 factorial design  
> experiment with
> males and females in each of the treatment groups (T1 & T2) measured  
> at multiple
> "events", each subject assigned an "id". The subjects are all  
> different ages so
> I would like to be able to control for the effect of "age range".
>
> If I didn't have "age range" as a covariate my model would be as  
> follows:
>
> anova x T1 T2 sex T1*T2 T1*sex T2*sex T1*T2*sex/id|T1*event T2*event  
> T1*T2*event
> sex*event sex*T1*event sex*T2*event T1*T2*sex*event, repeated(event)  
> partial
> bse(id|T1*T2*sex)
>
>
> Do I use the ANCOVA and cont(age range) command? Is this output the  
> effects of
> my fixed factors taking into account the effect of age range?
>
> --------------------------------------------------------------------------------
>
> First, the command line text shown doesn't look at all like correct  
> syntax.
> Second, by the name of it, a variable called "age range" would be  
> categorical
> and so you would not be using the -continuous()- option for it in - 
> anova-.
>
> Unless you have balanced data (equal representation of age ranges  
> within each
> factorial cell, as well as equal sex-by-treatment group cell sizes  
> maintained
> throughout the observation period), try something like the following  
> to start
> with:
>
> xi3 i.treatment_group*i.age_group*i.sex*i.observation_interval
> xtmixed response _I* || patient_id: , nolrtest variance reml
>
> You'll need to install the user-written command, -xi3-, from SSC if  
> you haven't
> already.
>
> Joseph Coveney
>
>
>
> *
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