[R] R^2 analogue in polr() and prerequisites for polr()

[Prof Brian Ripley]

On 8 Dec 2003, Christoph Lehmann wrote:

> (1)In polr(), is there any way to calculate a pseudo analogue to the
> R^2. Just for use as a purely descriptive statistic of the goodness of
> fit?

First define the statistic you are interested in!  There is an absolute 
measure of fit, the residual deviance.

> (2) And: what are the assumptions which must be fulfilled, so that the
> results of polr() (t-values, etc.) are valid? How can I test these
> prerequisites most easily: I have a three-level (ordered factor)
> response and four metric variables.

This is discussed with worked examples in the book that MASS supports, so 
please consult your copy.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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