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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Michael Lau > Sent: Wednesday, November 24, 2004 10:26 PM > To: [EMAIL PROTECTED] > 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 > > > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
