David, Thanks for the help. I missed the significance of the section you quoted below from the help. That does indeed solve the problem.
Dan Dan Nordlund Bothell, WA USA > -----Original Message----- > From: David Barron [mailto:[EMAIL PROTECTED] > Sent: Wednesday, January 24, 2007 3:32 AM > To: Daniel Nordlund; r-help > Subject: Re: [R] solving a structural equation model using sem or other > package > > This is an extract from the sem help page, which deals with your situation: > > S covariance matrix among observed variables; may be input as a > symmetric matrix, or as a lower- or upper-triangular matrix. S may > also be a raw (i.e., ``uncorrected'') moment matrix — that is, a > sum-of-squares-and-products matrix divided by N. This form of input is > useful for fitting models with intercepts, in which case the moment > matrix should include the mean square and cross-products for a unit > variable all of whose entries are 1; of course, the raw mean square > for the unit variable is 1. Raw-moment matrices may be computed by > raw.moments. > > On 24/01/07, Daniel Nordlund <[EMAIL PROTECTED]> wrote: > > I am trying to work my way through the book "Singer, JD and Willett, JB, > > Applied > Longitudinal Data Analysis. Oxford University Press, 2003" using R. I have > the SAS > code and S-Plus code from the UCLA site (doesn't include chapter 8 or later > problems). In chapter 8, there is a structural equation/path model which can > be > specified for the sem package as follows > > <<<snip>>> > > An equivalent specification in SAS produces the solution presented in the > > book. The > variable cons is a constant vector of 1's. The problem with the sem package > is that the > covariance matrix which includes the variable cons is singular and sem says > so and > will not continue. Is there an alternative way to specify this problem for > sem to obtain > a solution? If not, is there another package that would produce a solution? > > > > Thanks, > > > > Dan Nordlund > > Bothell, WA > > > > ______________________________________________ > > R-help@stat.math.ethz.ch 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. > > > > > -- > ================================= > David Barron > Said Business School > University of Oxford > Park End Street > Oxford OX1 1HP ______________________________________________ R-help@stat.math.ethz.ch 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.
