[R] Help with SEM package: Error message

lisamp85 lisamlpham at gmail.com
Tue Nov 8 17:18:28 CET 2011


I started using the sem package in R and after a lot of searching and trying
things I am still having difficulty.  I get the following error message when
I use the sem() function:

Warning message:
In sem.default(ram = ram, S = S, N = N, param.names = pars, var.names =
vars,  :
  Could not compute QR decomposition of Hessian.
Optimization probably did not converge.

I started with a simple example using the specify.model() function, but it
is really straight forward.  I uploaded my specify.model script and my data
covariance matrix here too so I wouldn't clutter this email with the entire
model (20 observed variables, 5 factors).  Could this error message be from
the data itself and not from my path model?

I have my observed variables X and my unobserved variables F.  I have ONLY
exogenous latent variables (i.e. they never appear on the right side of the
single head arrow ->).  I include all possible factor covariances FjFk, and
the only constraints I've made was to restrict the Factor variances to 1.
My model follows in this basic format (as you can see from my uploaded

# Factors (where I specify which observed variables load on to which
# I have only exogenous latent variables
F.i -> X.j, lamj.i, NA
# Observed variable variances
X.j <-> X.j, ej, NA
# Factor variances (I fixed all factor variances to 1)
F.i <-> F.i, NA, 1
# Factor covariances (I represent all factor covariances, i.e. the upper or
lower triangle of a covariance matrix)
F.i <-> F.k, FiFk, NA

Did I do something wrong here?  
Here are my uploaded files:
CFA script:  http://r.789695.n4.nabble.com/file/n4016569/CFA_script.txt
Covariance matrix: 

Thank you so much for any and all of your help.

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