[R] Difficulty understanding sem errors / failed confirmatory factor analysis
Adam D. I. Kramer
adik at ilovebacon.org
Thu Sep 18 19:01:30 CEST 2008
I'm trying to fit a pretty simple confirmatory factor analysis using
the sem package. There's a CFA example in the examples, which is helpful,
but the output for my (failing) model is hard to understand. I'd be
interested in any other ways to do a CFA in R, if this proves troublesome.
The CFA is replicating a 5 uncorrelated-factor structure (for those
interested, it is a structure of word usage patterns in weblogs) in a
special population. The model looks like model.txt (attached as many people
hate long emails); the correlation matrix cors.txt as well.
I'm setting no overlap between factors, no correlation between
factors, and estimating a separate variance for each observed variable
(which should be everything on the right-hand side of the -> arrows), but
setting the factor variances equal to 1...pretty standard. I've ensured that
everything is typed correctly to the best I am able.
model.kr <- specify.model(file="model.txt") # printing it checks out ok
correl <- read.csv("cors.csv", header=TRUE) # printing it checks out ok
kr.sem <- sem(ram=model.kr,S=correl,N=3034)
...about 10 seconds pass...
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.
(running qr on correl works fine; randomly-generated correl matrices fail in
the same way; I do not know how to further troubleshoot this)
...and then the model itself (which is produced, as the above was just a
Error in data.frame(object$coeff, se, z, 2 * (1 - pnorm(abs(z))), par.code) :
arguments imply differing number of rows: 47, 0
...both of these error messages are beyond my ability to troubleshoot. Any
help would be greatly appreciated. Because I am unsure what exactly the
problem with this analysis is, I can't create a simpler example for testing
purposes...but I think my model and correlation matrix are fairly simple.
"linux-gnu" "x86_64, linux-gnu"
svn rev language
"R version 2.7.2 (2008-08-25)"
...sem installed via install.packages("sem") which I assume is current.
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