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Re: st: Count data interaction terms

From   Maarten Buis <[email protected]>
To   [email protected]
Subject   Re: st: Count data interaction terms
Date   Tue, 23 Aug 2011 12:12:54 +0200

On Tue, Aug 23, 2011 at 11:40 AM, DA Gibson <[email protected]> wrote:
> Hi Maarten
> Thanks for that, i do have one further question however. In the
> example the IRR on the c.persons#c.child interaction term is positive
> at .77 however in your email you say that the interpretation is that
> the effect is reduced.

These effects are ratios rather than differences, so any number less
than 1 is a "negative" effect. If you multiply some number with a
number less than one, than the result will be smaller than the
original number. You can transform ratios into percentage changes by
doing (ratio - 1)*100%, i.e. multiplying the effect of persons by
0.77, is equivalent to saying that the effect of persons changes with
-23% when the extra person is a child.

Hope this helps,

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
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