[R] Marginal (type II) SS for powers of continuous variables in a linear model?

[Prof Brian Ripley]

On Tue, 12 Aug 2003, Bjørn-Helge Mevik wrote:

> Prof Brian D Ripley <ripley at stats.ox.ac.uk> writes:
> 
> > On Tue, 12 Aug 2003, [iso-8859-1] Bjørn-Helge Mevik wrote:
> 
> > Why should I(x^2) be regarded as subservient to x?
> 
> In polynomial regression, it is usual to first consider a linear
> model, then a quadratic, and so forth.  The interesting tests are usually
> then the effect of a power of x whith all lower degree terms of x in the
> model.  I thought it would be natural to treat polynomials of
> continuous variables similarly in models with categorical variables as
> well.

It would be, but I(x^2) is not associated with a polynomial.  It's
a deficiency of R/S that there is no simple way to do this, but if it 
were to be done it would be via the use of poly() (and you would only be 
able to frop the highest-degree term, not what you expressed as 
`marginal').

-- 
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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