Power calculation for repeated measures

[Nyougo Omae.]

Hello,

I am checking to see the power achieved in a handful of published papers to help inform some  research. So far, I've been able to calculate those of the t-tests (thanks for G*power). However, I am unable to get software that would calculate power given repeated measures statistics. (G*power has an option for the F statistic but I need correlations betweent the variables -- which has not been reported in any of the articles I am considering). Please help.

Thank you.

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[Marta Garcia-Granero]

Nyougo Omae. wrote:
> I am checking to see the power achieved in a handful of published papers to help inform some  research. So far, I've been able to calculate those of the t-tests (thanks for G*power). However, I am unable to get software that would calculate power given repeated measures statistics. (G*power has an option for the F statistic but I need correlations betweent the variables -- which has not been reported in any of the articles I am considering). Please help.
>
The program you need is MorePower, specifically designed for ANOVA
models, either with between or within subjects effects. The web page has
a link to a document that shows how to use it with SPSS output.

http://homepage.usask.ca/~jic956/work/MorePower.html

HTH,
Marta García-Granero


--
For miscellaneous statistical stuff, visit:
http://gjyp.nl/marta/

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[Sara House]

Nyougo Omae. wrote:
> I am checking to see the power achieved in a handful of published papers to help inform some  research. So far, I've been able to calculate those of the t-tests (thanks for G*power). However, I am unable to get software that would calculate power given repeated measures statistics. (G*power has an option for the F statistic but I need correlations betweent the variables -- which has not been reported in any of the articles I am considering). Please help.
I'm not sure, but you might still need correlations between the variables (between the time1 and time2 measures) regardless of what program you're using.  This information is not often reported, but you can obtain such information (sometimes) from other sources.  The correlation between time1 and time2 should be approximately equal to test-retest reliability, and this information could be obtained from the author of the measure being used.
 
Sara
 
 
Sara M. House, M.A.
Adjunct Faculty
Loyola University Chicago, Psychology Department
Email: [hidden email]
Teaching: Research Methods, Psychology & Law

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[SR Millis-3]

If you have a relatively complex mixed model design, Opitmal Design software will be helpful:


http://sitemaker.umich.edu/group-based/optimal_design_software



Scott R Millis, PhD, MEd, ABPP (CN,CL,RP), CStat
Professor & Director of Research
Dept of Physical Medicine & Rehabilitation
Wayne State University School of Medicine
261 Mack Blvd
Detroit, MI 48201
Email:  [hidden email]
Tel: [phone]
Fax: [phone]


--- On Thu, 10/9/08, Marta García-Granero <[hidden email]> wrote:

> From: Marta García-Granero <[hidden email]>
> Subject: Re: Power calculation for repeated measures
> To: [hidden email]
> Date: Thursday, October 9, 2008, 12:28 PM
> Nyougo Omae. wrote:
> > I am checking to see the power achieved in a handful
> of published papers to help inform some  research. So far,
> I've been able to calculate those of the t-tests (thanks
> for G*power). However, I am unable to get software that
> would calculate power given repeated measures statistics.
> (G*power has an option for the F statistic but I need
> correlations betweent the variables -- which has not been
> reported in any of the articles I am considering). Please
> help.

=====================
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[Swank, Paul R]

This is only useful if the time between t1 and t2 is approximately the
same as the time for the test-retest. If t1 and t2 differ by a year and
the test-retest reliability is over two weeks then you would seriously
overestimate the correlation.

Paul R. Swank, Ph.D
Professor and Director of Research
Children's Learning Institute
University of Texas Health Science Center
Houston, TX 77038


-----Original Message-----
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of
Sara House
Sent: Thursday, October 09, 2008 11:35 AM
To: [hidden email]
Subject: Re: Power calculation for repeated measures

Nyougo Omae. wrote:
> I am checking to see the power achieved in a handful of published
papers to help inform some  research. So far, I've been able to
calculate those of the t-tests (thanks for G*power). However, I am
unable to get software that would calculate power given repeated
measures statistics. (G*power has an option for the F statistic but I
need correlations betweent the variables -- which has not been reported
in any of the articles I am considering). Please help.
I'm not sure, but you might still need correlations between the
variables (between the time1 and time2 measures) regardless of what
program you're using.  This information is not often reported, but you
can obtain such information (sometimes) from other sources.  The
correlation between time1 and time2 should be approximately equal to
test-retest reliability, and this information could be obtained from the
author of the measure being used.

Sara


Sara M. House, M.A.
Adjunct Faculty
Loyola University Chicago, Psychology Department
Email: [hidden email]
Teaching: Research Methods, Psychology & Law

==========To manage your subscription to SPSSX-L, send a message to
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=====================
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