
 
Effectively in this situation I am working with the function sem in the package sem
I will try this parameter fix.c
 
Thanks a lot 


Antra EL MOUSSELLY 


 


Date: Mon, 28 Mar 2011 12:42:31 -0700
From: ml-node+3412847-1368787395-225466@n4.nabble.com
To: antrael@hotmail.com
Subject: Re: Structural equation modeling in R(lavaan,sem)

Dear jouba, 

I think you're using the sem() function in the sem package. 

I'm not sure that I understand your question, but I think it is why you need to specify the variance of the exogenous variable x1 as a parameter. The answer is that it is a parameter to be estimated from the data, but you can avoid specifying it explicitly by using the fixed.x argument to sem(). 

I hope this helps, 
 John 

On Mon, 28 Mar 2011 09:00:05 -0700 (PDT) 
 jouba <[hidden email]> wrote: 

> 
>   
> Dear all , 
> I am trying to run sem by an example with my data but i have problme with an  exogen variable  x1 so my examlpe is below 
> when i add i the equation we have no pboblem but i donâ€™t know why ?? 
>   
> x1 <->x1, sigmma7, NA 
> for me this  an exogen variable and i am not obliged to specify this equation 
>   
> model.se<-specify.model() 
> x1->x2,gamm1,NA 
> x2->x3,gamm2,NA 
> x3>x4,gamm3,NA 
> x4->x5,gamm4,NA 
> x7->x6,gamm5,NA 
> x6->x5,gamm6,NA 
> x2 <->x2 ,sigmma1,NA 
> x3 <->x3 ,simma2,NA 
> x4 <->x4 ,sigmma3,NA 
> x5 <->x5 ,sigmma4,NA 
> x7 <->x7 ,sigmma5,NA 
> x6 <->x6 ,sigmma6,NA 
>   
> sem.se <- sem(model.se, cov(se), 245) 
> Erreur dans solve.default(C) : 
>   sous-programme Lapack dgesv : le systÃ¨me est exactement singulier 
> De plus : Message d'avis : 
> In sem.default(ram = ram, S = S, N = N, param.names = pars, var.names = vars,  : 
>   The following variables have no variance or error-variance parameter (double-headed arrow): 
>  x1 
> The model is almost surely misspecified; check also for missing covariances. 
>   
> Thanks a lot 
> 
> 
> Antra EL MOUSSELLY 
> 
> 
>   
> 
> 
> Date: Mon, 28 Mar 2011 05:40:32 -0700 
> From: [hidden email] 
> To: [hidden email] 
> Subject: Re: Structural equation modeling in R(lavaan,sem) 
> 
> 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 
> 
> ______________________________________________ 
> [hidden email] 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. 
> 
> 
> 
> 
> 
> 
> If you reply to this email, your message will be added to the discussion below:http://r.789695.n4.nabble.com/Structural-equation-modeling-in-R-lavaan-sem-tp3409642p3411579.html  
> To unsubscribe from Structural equation modeling in R(lavaan,sem), click here.       
> 
> -- 
> View this message in context: http://r.789695.n4.nabble.com/Structural-equation-modeling-in-R-lavaan-sem-tp3409642p3412181.html
> Sent from the R help mailing list archive at Nabble.com. 
> [[alternative HTML version deleted]] 
> 
------------------------------------------------ 
John Fox 
Sen. William McMaster Prof. of Social Statistics 
Department of Sociology 
McMaster University 
Hamilton, Ontario, Canada 
http://socserv.mcmaster.ca/jfox/

______________________________________________ 
[hidden email] 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. 






If you reply to this email, your message will be added to the discussion below:http://r.789695.n4.nabble.com/Structural-equation-modeling-in-R-lavaan-sem-tp3409642p3412847.html 
To unsubscribe from Structural equation modeling in R(lavaan,sem), click here.  		 	   		  

--
View this message in context: http://r.789695.n4.nabble.com/Structural-equation-modeling-in-R-lavaan-sem-tp3409642p3413316.html
Sent from the R help mailing list archive at Nabble.com.
	[[alternative HTML version deleted]]

