Re: st: Interactions in xreg

[Morten Hesse <mh@crf.au.dk>]

Den 23-08-2010 12:33, Maarten buis skrev:
> --- On Mon, 23/8/10, Morten Hesse wrote:
> > I did that too, and it works. "Block" is of course an
> > ordinal variable (1-5). Yet, I want to test whether
> > the group with characteristic "ant" has a different
> > pattern of behaviour over "blocks", and I have reasons
> > to believe that that pattern is curvilinear, compared
> > with subjects who do net have characteristic "ant"
> > (scores increases towards the middle, of the test,
> > decreases towards the end). I can of course test
> > whether the parameter for subjects during the
> > different blocks are significant (e.g., start versus
> > middle, and middle  versus start). And indeed, they
> > are. But I have never seen that used as  a test of
> > curvilinearity, and I feel that it is a bit "informal".
> > Am I wrong?
> Yes, unfortunately you are wrong. Such quadratic terms
> have no meaning in an ordinal variable. If you do so
> you are basically assuming that the distances between
> your 5 categories are equal.
>
> -- Maarten
>
> --------------------------
> Maarten L. Buis
> Institut fuer Soziologie
> Universitaet Tuebingen
> Wilhelmstrasse 36
> 72074 Tuebingen
> Germany
>
> http://www.maartenbuis.nl
> --------------------------
>
>
>
>
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