[R] logistic regression and 3PL model

[John Fox]

Dear Mike,

Pinheiro and Bates discuss a three-parameter logistic growth model in their
Mixed Effects Models in S and S-PLUS, but as far as I know there's no direct
way to fit the 3PL IRT model in R. It should be possible to fit such a model
using one of the general optimisers in R, such as nlm() or optimise(), and I
think that it would be a nice project to produce an IRT package for R. 

Regards,
 John

--------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4
905-525-9140x23604
http://socserv.mcmaster.ca/jfox 
-------------------------------- 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Michael Lau
> Sent: Wednesday, November 24, 2004 10:26 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] logistic regression and 3PL model
> 
> Hello colleagues,
> 
>  
> 
> I am a novice with R and am stuck with an analysis I am 
> trying to conduct.
> Any suggestions or feedback would be very much appreciated.
> 
>  
> 
> I am analyzing a data set of psi (ESP) ganzfeld trials.  The 
> response variable is binary (correct/incorrect), with a 25% 
> base rate.  I've looked around the documentation and other 
> online resources and cannot find how I can correct for that 
> base rate when I conduct a logistic regression.  I understand 
> that the correction would be equivalent to the three 
> parameter logistic model (3PL) in IRT but am unsure how to 
> best fit it from a logistic regression in R.
> 
>  
> 
> Thanks much,
> 
>  
> 
> Mike Lau
> 
>  
> 
> __________________________________
> Michael Y. Lau, M.A. 
> 118 Haggar Hall
> Department of Psychology
> University of Notre Dame
> Notre Dame, IN 46556 
>  
>   
> 
>  
> 
> 
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> 
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