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Re: st: power repeated measures anova vs mixed models


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: power repeated measures anova vs mixed models
Date   Thu, 24 May 2012 12:59:54 -0400

Ricardo Ovaldia <ovaldia@yahoo.com>:
Of course what you plug in matters--see also:
http://www.urban.org/UploadedPDF/1001394-clustered-randomization.pdf
(esp. page 6) and references therein.
You need estimates for the relevant information before you can estimate power.

On Thu, May 24, 2012 at 12:39 PM, Ricardo Ovaldia <ovaldia@yahoo.com> wrote:
> Thank you David.
> I played with this a few day ago. The problem is that you have to make a lot of assumptions that I do not feel comfortably making because I lack prior knowledge about parameters, covariances, etc. The program produces very different results depending on what you "plug in".
>
> Ricardo
>
> Ricardo Ovaldia, MS
> Statistician
> Oklahoma City, OK
>
>
> --- On Thu, 5/24/12, Airey, David C <david.airey@vanderbilt.edu> wrote:
>
>> From: Airey, David C <david.airey@vanderbilt.edu>
>> Subject: re: st: power repeated measures anova vs mixed models
>> To: "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
>> Date: Thursday, May 24, 2012, 10:01 AM
>> .
>>
>> I just came across this software for longitudinal /
>> hierarchical experimental design power analysis:
>>
>> http://sitemaker.umich.edu/group-based/optimal_design_software
>>
>> I've not used it, but it might help you avoid simulation.
>>
>> -Dave
>>
>> > Dear all,
>> >
>> > I have been struggling to find an answer or reference
>> to this problem.
>> >
>> > I am planning a longitudinal analysis comparing 3
>> groups with 6 time points per subject. The design is balance
>> with 65 subjects for group.
>> >
>> > Because I do not have preliminary data and do not want
>> to make unrealistic assumptions about the covariate
>> structure and other parameters required to calculate power
>> for mixed models, I decided to use repeated measures ANOVA
>> to estimate the minimum detectable effect size at 80% power.
>>
>> > My questions are, will the mixed model have more power
>> that the repeated measures ANOVA in this case? Are there any
>> references regarding these comparisons?
>> >
>> > Thank you,
>> > Ricardo
>> >
>> > Ricardo Ovaldia, MS
>> > Statistician
>> > Oklahoma City, OK

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