From: Daniel Nordlund <res90sx5_at_verizon.net>

Date: Wed 24 Jan 2007 - 15:47:59 GMT

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. Received on Thu Jan 25 13:06:02 2007

Date: Wed 24 Jan 2007 - 15:47:59 GMT

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:mothsailor@googlemail.com]
**> 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 <res90sx5@verizon.net> 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
*

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