[R] Power calculation with measurement error

[Mike Lawrence]

Thanks Greg, I've actually been programming precisely what you  
suggest since sending the request this morning (though your email was  
indeed helpful; I've never seen 'replicate()' and will see if it's  
faster than a loop).

However, I was hoping that an analytic solution was extant and  
implemented somewhere.


On 26-Jun-07, at 12:18 PM, Greg Snow wrote:

> I don't know of a current package that does this (others may), but if
> you know what you expect your data to look like you can simulate it  
> and
> calculate power that way.
>
> Basically, write a function that will simulate data with the level of
> measurement error that you expect in the real data (or have the amount
> of measurement error passed in as a parameter so you can examine the
> effect of diffenent values).  Then have the function compute the t  
> test
> (or other test that you plan to do) and return the p-value from the
> test.
>
> Then you can simulate the process with a command like:
>
>> out1 <- replicate( 1000, myfunction(n=25, err=.1, diff=.5) )
>
> And compute the power with:
>
>> mean( out1 < 0.05 ) # or whatever alpha value you want.
>
> Hope this helps,
>
> -- 
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at intermountainmail.org
> (801) 408-8111
>
>
>
>> -----Original Message-----
>> From: r-help-bounces at stat.math.ethz.ch
>> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Mike Lawrence
>> Sent: Tuesday, June 26, 2007 5:13 AM
>> To: Rhelp
>> Subject: [R] Power calculation with measurement error
>>
>> Hi all,
>>
>> Hopefully this will be quick, I'm looking for pointers to
>> packages/ functions that would allow me to calculate the
>> power of a t.test when the DV has measurement error. That is,
>> I understand that, ceteris paribus, experiments using measure
>> with more error (lower
>> reliability) will have lower power.
>>
>> Mike
>>
>> --
>> Mike Lawrence
>> Graduate Student, Department of Psychology, Dalhousie University
>>
>> Website: http://memetic.ca
>>
>> Public calendar: http://icalx.com/public/informavore/Public
>>
>> "The road to wisdom? Well, it's plain and simple to express:
>> Err and err and err again, but less and less and less."
>> 	- Piet Hein
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>>
>

--
Mike Lawrence
Graduate Student, Department of Psychology, Dalhousie University

Website: http://memetic.ca

Public calendar: http://icalx.com/public/informavore/Public

"The road to wisdom? Well, it's plain and simple to express:
Err and err and err again, but less and less and less."
	- Piet Hein