Specifying Path Model in SEM for CFA
On Wed, 2006-08-16 at 17:01 -0400, John Fox wrote:
Dear Rick, It's unclear to me what you mean by constraining "each column of the factor matrix to sum to one." If you intend to constrain the loadings on each factor to sum to one, sem() won't do that, since it supports only equality constraints, not general linear constraints on parameters of the model, but why such a constraint would be reasonable in the first place escapes me. More common in confirmatory factor analysis would be to constrain more of the loadings to zero. Of course, one would do this only if it made substantive sense in the context of the research. Regards, John -------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario Canada L8S 4M4 905-525-9140x23604 http://socserv.mcmaster.ca/jfox --------------------------------
I'm trying to build a multivariate receptor model as described by Christensen and Sain (Technometrics, vol 44 (4) pp. 328-337). The model is x_t = Af_t + e_t where A is the matrix of nonnegative source compositions, x_t are the observed pollutant concentrations at time t, and f_t are the unobserved factors. The columns of A are supposed to sum to no more than 100%. They say they are using a latent variable model. If sem can't handle this, do you know of another R package that could? Rick B.