Re: [R] sample size determination

From: Martin Henry H. Stevens <HStevens_at_MUOhio.edu>
Date: Wed 19 Oct 2005 - 06:09:26 EST

?power.anova.test is designed for 1 way models. I would be intrigued to found out more about power in complicated designs. Do look into the archives at
http://finzi.psych.upenn.edu/search.html   In the past, I used power.t.test on individual model coefficients, though I am not sure it was correct.
Hank Stevens

On Oct 18, 2005, at 3:50 PM, Chris Behr wrote:

> Hello,
>
> I am a new user of R and trying to assess the sample size for data
> that is
> being collected on water quality at sites across a wide geographic
> region. A
> preliminary set of data has been collected and I would like to use
> it to
> assess whether we are collecting enough data and in the right places.
>
> A factorial approach was initially used to characterize sites by
> well type,
> latrine type, distance between well and latrine, and ecological
> region.
> Altogether the basic structure has:
>
> 3 types of wells
> 3 types of latrines
> 4 distance categories
> 13 regions
>
> We define a “site-type” as: a well-latrine-distance combination.
> There are
> 36 of these. A number of replicates (between 1 and 4) of the 36
> site-types
> are included in the set of sites in each of the 13 regions. Some
> regions
> have more replicates than others due to complexity in the region.
> In total
> there are 936 sites.
>
> At this point, I have an ANOVA model with water quality measures
> and only
> (these) categorical data. I want to know if I am collecting enough
> samples
> (given alpha and beta levels) to see if there are effects for wells,
> latrines, distances, and region (independently), as well as
> interactions for
> well-distance, well-latrine, and well-region. I would like to also
> perform a
> power analysis to allow the power vary with sample size.
>
> I am working my way through various texts and help functions but
> thought I
> would see if anyone else has learned how to do this already.
>
> I would appreciate any and all guidance.
>
> Best wishes, Chris
>
> Christopher Behr
> Principal Analyst
>
> eDesign Dynamics
> www.edesigndynamics.com
> Christopher Behr
> Principal Analyst
>
> eDesign Dynamics
> www.edesigndynamics.com
>
> 4024 Calvert St. NW
> Washington DC 20007
> (202) 298-6437 (t/f)
> (551) 998-4823 (c)

>
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Dr. Martin Henry H. Stevens, Assistant Professor 338 Pearson Hall
Botany Department
Miami University
Oxford, OH 45056

Office: (513) 529-4206
Lab: (513) 529-4262
FAX: (513) 529-4243

http://www.cas.muohio.edu/~stevenmh/
http://www.muohio.edu/ecology/
http://www.muohio.edu/botany/

"E Pluribus Unum"

R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Oct 19 06:18:37 2005

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