Dear Manuel, Polychoric correlations imply only that the *latent* variables are continuous -- the observed variables are ordered categories. Tetrachoric and point-biserial correlations are special cases respectively of polychoric and polyserial correlations. As long as you're willing to think of the dichotomous variable as the dissection into two categories of a latent continuous variable (and assuming multinormality of the latent variables), you can use the approach that I suggested. This isn't logistic regression, but it's similar to a probit model.
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 Manel Salamero > Sent: Sunday, August 14, 2005 12:34 PM > To: [email protected] > Subject: Re: [R] path analysis > > This solves part of my problem with the independent ordinal > variables, but my dependent variable is truly categorial > (illness/no illness). Polychoric correlation implies that > data are continuous, which in not the case. Is possible to > implement logistic regression in the path model? > > Thanks, > > Manel Salamero > > ---------- Original Message ---------------------------------- > De: "John Fox" <[EMAIL PROTECTED]> > Data: Sat, 13 Aug 2005 19:35:24 -0400 > > Dear Manel, > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of > SALAMERO BARO, > > MANUEL > > Sent: Saturday, August 13, 2005 2:02 PM > > To: [email protected] > > Subject: [R] path analysis > > > > Someone knows if it is possible to perform a path analysis with sem > > package (or any other) to explain a dependent > > *dichotomus* variable? > > > > Yes -- you can use the hetcor() function in the polycor > package to generate > a correlation matrix and boot.sem() in the sem package to get standard > errors or confidence intervals. Make sure that the > dichotomous variables are > represented as factors. See ?boot.sem for an example. > > I hope this helps, > John > > ______________________________________________ > [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
