Problems bootstrapping multigroup SEM

Dear Chad,

It's possible that I don't understand properly what you've done, but it appears as if you're passing to bootSem() the covariance matrices for the observed data rather than the case-by-variable data sets themselves. That's also what you say you're doing, and it's what the error message says. 

Moreover, if you look at the documentation in ?bootSem, you'll is that the Cov argument isn't a covariance matrix, but "a function to compute the input covariance or moment matrix; the default is cov. Use cor if the model is fit to the correlation matrix. The function hetcor in the polycor package will compute product-moment, polychoric, and polyserial correlations among mixed continuous and ordinal variables (see the first example below for an illustration)."

So what is there to bootstrap if bootSem() doesn't have access to the original data sets? I suppose that one could do a parametric bootstrap of some sort, but that's not what bootSem() does -- in implements a nonoparametric bootstrap, which requires the original data.

I hope this helps,
 John

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John Fox, Professor
McMaster University
Hamilton, Ontario, Canada
http://socserv.socsci.mcmaster.ca/jfox/

Problems bootstrapping multigroup SEM

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