On 03/28/2011 04:18 AM, jouba wrote:
Jeremy thanks a lot for your response I have read sem package help and I currently reading the help of lavaan I see that there is also an other function called lavaan can do the SEM analysis So I wonder what is the difference between this function and the sem function
The 'sem()' function (in the lavaan package) is more user-friendly, in the sence that it sets a number of reasonable options by default, before calling the lower-level 'lavaan()' function (which has the 'feature' of doing nothing automatically, but expects that you really know what your are doing).
Most users should only use the 'sem()' function (or the 'cfa()' function). For non-standard models, the 'lavaan()' function gives more control.
Also I am wondering in the case where we have categorical variables and discreet variables??
Currently, the lavaan package (0.4-7) has no support for categorical variables.
calculate the correlation matrix , mainly when we have to calculate these between a quantitative and qualitative variables, I wonder if polycor package is the best solution for this
It depends. The 'hetcor()' function in the polycor package may provide a suitable correlation matrix that can be used with the 'sem' package or the 'lavaan' package. However, AFAIK, the polycor does not compute the corresponding asymptotic weight matrix which you need for getting proper standard errors and test statistics (in a WLS context).
The OpenMx package (http://openmx.psyc.virginia.edu/) has some support for categorical (ie binary/ordinal) observed variables (although I'm not sure if they can handle the joint analysis of ordinal and continuous variables yet).
But none of this is needed _if_ the categorical variables are all exogenous (ie predictor variables only) in which case you can still use the methods for continuous data.
Yves. -- Yves Rosseel -- http://www.da.ugent.be Department of Data Analysis, Ghent University Henri Dunantlaan 1, B-9000 Gent, Belgium ______________________________________________ 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.
