[R] Power of t test for unequal variances?

[Mauricio Cornejo]

David,
I was not aware I could search through the list of available packages.  Thanks very much for the tip.
Regarding your guidance that my question may not have been appropriate for R-help as it may not have been specifically an R question ... since it seemed like an R question to me, are there any particular criteria that would help me determine if my question is sufficiently specific to R to be appropriate for R-help?
Thanks again,
Mauricio 

    On Monday, December 19, 2016 10:14 PM, David Winsemius <dwinsemius at comcast.net> wrote:
 
 
> On Dec 19, 2016, at 3:31 PM, David Winsemius <dwinsemius at comcast.net> wrote:
> 
> 
>> On Dec 19, 2016, at 1:47 PM, Mauricio Cornejo via R-help <r-help at r-project.org> wrote:
>> 
>> Is there a function similar to stats::power.t.test that can handle unequal variances from two samples?
>> I noticed that stats::t.test has an argument for indicating whether or not to treat the two sample variances as equal.  Wondering why stats::power.t.test doesn’t have that option.
>> Thanks,Mauricio
>>     [[alternative HTML version deleted]]
> 
> Because R was developed by statisticians for statisticians and they assumed those other statisticians would know how to extend its functions when needed. But R-help is not advertised as the place to ask such questions when you don't have the statistical skills. (You might want to look at the code of `t.test` to see how you might construct appropriate arguments for `power.t.test` in the situation you imagine. Seems to me it should be fairly straightforward. `power.t.test` is built around the non-central t-distribution and solves a uniroot problem for the missing parameter among  n, delta, power, sd, and sig.level, given the other 4 parameters.)
> 

The other R-specific response might have been to teach you to use R's functions to do a bit of searching:

 ?available.packages
 old.opt <- options(available_packages_filters =
                              c("R_version",  "CRAN", "duplicates"))
 # saved options from prior state

 avail <- available.packages()
 names(avail)
NULL  # oops, not a list.
> str( avail)
 chr [1:9731, 1:17] "A3" "abbyyR" "abc" "ABCanalysis" ...
 - attr(*, "dimnames")=List of 2
  ..$ : chr [1:9731] "A3" "abbyyR" "abc" "ABCanalysis" ...
  ..$ : chr [1:17] "Package" "Version" "Priority" "Depends" ...
 colnames(avail)
#--- result---
 [1] "Package"              "Version"              
 [3] "Priority"              "Depends"              
 [5] "Imports"              "LinkingTo"            
 [7] "Suggests"              "Enhances"            
 [9] "License"              "License_is_FOSS"      
[11] "License_restricts_use" "OS_type"              
[13] "Archs"                "MD5sum"              
[15] "NeedsCompilation"      "File"                
[17] "Repository"        
#---------  


 avail[ grepl("pow" ,avail[ ,"Package"] , ignore.case=TRUE), "Package"]
                asypow          bivarRIpower          clusterPower 
              "asypow"        "bivarRIpower"        "clusterPower" 
            easypower                  fpow              longpower 
          "easypower"                "fpow"            "longpower" 
                matpow              mnormpow              PharmPow 
              "matpow"            "mnormpow"            "PharmPow" 
                powell                  PoweR            Power2Stage 
              "powell"                "PoweR"          "Power2Stage" 
        powerAnalysis          powerbydesign  powerGWASinteraction 
      "powerAnalysis"        "powerbydesign" "powerGWASinteraction" 
              poweRlaw        powerMediation              powerpkg 
            "poweRlaw"      "powerMediation"            "powerpkg" 
            powerplus          powerSurvEpi              PowerTOST 
          "powerplus"        "powerSurvEpi"            "PowerTOST" 
              PowerUpR      rPowerSampleSize      twoStageGwasPower 
            "PowerUpR"    "rPowerSampleSize"    "twoStageGwasPower" 

A more usable result:

 names( avail[ grepl("pow" ,avail[ ,"Package"] , ignore.case=TRUE), "Package"] )
 [1] "asypow"              "bivarRIpower"        
 [3] "clusterPower"        "easypower"          
 [5] "fpow"                "longpower"          
 [7] "matpow"              "mnormpow"            
 [9] "PharmPow"            "powell"              
[11] "PoweR"                "Power2Stage"        
[13] "powerAnalysis"        "powerbydesign"      
[15] "powerGWASinteraction" "poweRlaw"            
[17] "powerMediation"      "powerpkg"            
[19] "powerplus"            "powerSurvEpi"        
[21] "PowerTOST"            "PowerUpR"            
[23] "rPowerSampleSize"    "twoStageGwasPower"  

 options(old.opt)  # reset options to default values

So you may find additional user-contributed power-oriented packages.



> 
> -- 
> 
> David Winsemius
> Alameda, CA, USA
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius
Alameda, CA, USA


   
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