[R] logistic regression and 3PL model
Dimitris Rizopoulos
dimitris.rizopoulos at med.kuleuven.ac.be
Thu Nov 25 17:51:30 CET 2004
I don't know if I am missing something, but isn't there also a latent
variable (trait) that must be integrated out using maybe Gauss-Hermite
which might complicate a bit the calculations? So is this possible
with `glm()'?
Best,
Dimitris
----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat
http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
----- Original Message -----
From: "Prof Brian Ripley" <ripley at stats.ox.ac.uk>
To: "John Fox" <jfox at mcmaster.ca>
Cc: <r-help at stat.math.ethz.ch>
Sent: Thursday, November 25, 2004 5:13 PM
Subject: RE: [R] logistic regression and 3PL model
> On Thu, 25 Nov 2004, John Fox wrote:
>
>> 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
>
> optim(), not optimize() as there are at least two free parameters, I
> believe.
>
>> think that it would be a nice project to produce an IRT package for
>> R.
>
> As I understand it this is a logistic regression and not a logistic
> growth curve, the latter being fitted by least squares.
>
> For a known baseline (which is thus a 2-free PL model but what seems
> asked for here), a glm family can be constructed to allow glm() to
> do the fitting. This is model described at
>
> http://work.psych.uiuc.edu/irt/modeling_dich1.asp
>
> with c known to be 0.25. It would certainly be worth having an
> implementation of that in R, with c=0.5 being the most common case.
>
> It is quite straightforward to fit such models by direct
> optimization of the likelihood, and MASS4 p. 445 gives you a
> template for logistic regression that could easily be modified.
>
>
>>> -----Original Message-----
>>> 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.
>
> --
> Brian D. Ripley, ripley at stats.ox.ac.uk
> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
> University of Oxford, Tel: +44 1865 272861 (self)
> 1 South Parks Road, +44 1865 272866 (PA)
> Oxford OX1 3TG, UK Fax: +44 1865 272595
>
> ______________________________________________
> R-help at 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
>
More information about the R-help
mailing list