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Re: st: Stata journal paper on interaction terms in count models

From   Maarten Buis <>
Subject   Re: st: Stata journal paper on interaction terms in count models
Date   Tue, 14 May 2013 10:51:45 +0200

On Thu, May 9, 2013 at 4:46 PM, James Bernard wrote:
> The more I read the more confused I get.... I don't understand why a
> subject so close to mathematics (not exactly math) can be so confusing
> to every one
> Perhaps the problem is that statistics/econometrics is becoming too vast

I think that part of the problem is just conceptual: an effect is
simply a comparison of groups while an interaction is a comparison of
comparisons. The latter is as a consequence a step further removed
from the stuff we see (the data) and thus harder to visualize. Another
part of the problem is that non-linear models are non-linear. The way
to solve that is to take the non-linearity seriously and report
(interaction) effects in the natural metric of that model. In case of
a log link function (like in a Poisson model) you need to think in
terms of ratios rather than differences. Once you do that everything
becomes a lot simpler, as I showed earlier in this thread.

-- Maarten

Maarten L. Buis
Reichpietschufer 50
10785 Berlin
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