The problem is not in the book nor the code, but in Mr Carstensen not looking up the actual reference given in ?polr.
There was a + in early printings of MASS3, and that difference is in the on-line Errata. But both the DESCRIPTION file and ?polr are explicitly to the fourth edition. As Thomas says, the minus seemed a more natural parametrization and so we changed to it. On Thu, 8 Jan 2004, Thomas Lumley wrote: > On Thu, 8 Jan 2004, BXC (Bendix Carstensen) wrote: > > > In Venables \& Ripley 3rd edition (p. 231) the proportional odds model > > is described as: > > > > logit(p<=k) = zeta_k + eta > > > > but polr apparently thinks there is a minus in front of eta, > > as is apprent below. > > > > Is this a bug og a feature I have overlooked? > > If there is really a bug I would guess that it was in the book rather than > the code. This is not an unusual parametrisation for this model. It is > the parametrisation that reduces to logistic regression for binary data, > and makes the regression coefficients positive when the association is > positive. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
