Re: st: Posthoc power analysis for linear mixed effect model

[Jeph Herrin <info@flyingbuttress.net>]

I think this better explains the approach:

  http://www.stata-journal.com/sjpdf.html?articlenum=st0010

cheers,
jeph

On 3/7/2014 3:58 PM, Lance Erickson wrote:
> Jeph,
>
> Is the content at this link to the UCLA help pages (http://www.ats.ucla.edu/stat/stata/code/simulate.htm) a reasonable example of the approach you take? I'm referring to the first of the two examples they show.
>
> By '"known" true value' do you mean the coefficients estimated from the existing data?
>
> Thanks,
> Lance
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Jeph Herrin
> Sent: Friday, March 07, 2014 1:29 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: Posthoc power analysis for linear mixed effect model
>
> Generally, I usually do these using simulation.  That is, simulate a large number of datasets similar to the one you have but with values generated by a random process based on a "known" true value. Then to see how much power the model has, calculate the proportion of datasets where the model rejects the null hypothesis. -xtmixed- will take a while to run on all of the datasets, but it's not too bad if you only have one effect you want to estimate the power to detect.
>
> hth,
> Jeph
>
>
> On 3/7/2014 2:55 PM, Mohammod Mostazir wrote:
> > Dear great stat-warriors,
> >
> > I need some Stata related H--E--L--P here. I have a dataset that has
> > repeated BMI (Body Mass Index; continuous scale) measurements of 10
> > equally spaced annual time points from 140 cases. The interest is to
> > observed change in BMI in relation to other time-constant and
> > time-varying co-variates. The analysis I have carried out is linear
> > mixed effect model using Stata's 'xtmixed' command with random
> > intercepts and slopes.  Now I would like to carry out a posthoc power
> > analysis to see how much power the study has. Is there any light in
> > Stata in relation to this? I have seen Stata's ''power repeated''
> > command which does not suit here as they are suitable for one/two way
> > repeated ANOVA designs.
> >
> > Any comment is highly appreciated. Thanks for reading.
> >
> > Best,
> >
> > Mos
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