Dear Kesinee, > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > On Behalf Of Kes > Sent: March-07-11 9:51 PM > To: r-help@r-project.org > Subject: [R] SEM error > > Dear All, > I am new for R and SEM. I try to fit the model with Y (ordinal outcome), > X > (4 categorical data), M1-M3 (continuous), and 2 covariates (Age&sex) as > a diagram. > library(polycor) > model.ly <-specify.model() > 1: x -> m1, gam11, NA > 2: x -> m2, gam12, NA > 3: x -> m3, gam13, NA > 4: age -> m1, gam14, NA > 5: age -> m2, gam15, NA > 6: age -> m3, gam16, NA > 7: sex -> m1, gam17, NA > 8: sex -> m2, gam18, NA > 9: sex -> m3, gam19, NA > 10: x -> y, gam20, NA > 11: m1 -> y, gam21, NA > 12: m2 -> y, gam22, NA > 13: m3 -> y, gam23, NA > 14: age -> y, gam24, NA > 15: sex -> y, gam25, NA, > 16: m1 <->m1, psi11, NA > 17: m2 <-> m2, psi12, NA > 18: m3 <-> m3, psi13, NA > 19: m1 <-> m2, psi21, NA > 20: m1 <->m3, psi22, NA > 21: m2 <-> m3, psi23, NA > 22: Y <-> Y, psi24, NA, > > hcor <-function(ly) hetcor(ly, std.err=FALSE)$correlations R.ly <- > hcor(ly) sem.ly <- sem(model.ly, R.ly, N=174) > > Error in sem.default(ram=ram, S=S, N=N,…………………………) The model has > negative degree of freedom = -12 > > First, I do not know what the mistake is. Second, is this correctly > modeling my diagram? Any suggestions would be appreciated.
First, if x isn't ordinal, you have to create dummy regressors to represent it. Second, your model has no variances or covariances for the exogenous variables (which you could handle compactly with the fixed.x argument to sem). Third, I notice that you use both y and Y in the model. Since Y probably doesn't exist in the input data, sem() treats it as a latent variable. This probably produces the negative df, though I don't know off hand why; had you spelled y correctly, the df should be positive, although, as I've mentioned, the model makes no sense. Finally, this model has a block-recursive structure, and an alternative would be to fit each equation in the model as an appropriate regression model. I hope this helps, John -------------------------------- John Fox Senator William McMaster Professor of Social Statistics Department of Sociology McMaster University Hamilton, Ontario, Canada http://socserv.mcmaster.ca/jfox > > Thank you, > Kesinee > http://r.789695.n4.nabble.com/file/n3340497/path.gif.png > > -- > View this message in context: http://r.789695.n4.nabble.com/SEM-error- > tp3340497p3340497.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
