[R] sample size determination

[Martin Henry H. Stevens]

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

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