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# Re: st: state trends

 From sara borelli <[email protected]> To [email protected] Subject Re: st: state trends Date Tue, 19 Oct 2010 20:46:49 +0100 (BST)

```Thank you very much,
sara

--- Mar 19/10/10, Maarten buis <[email protected]> ha scritto:

> Da: Maarten buis <[email protected]>
> Oggetto: Re: st: state trends
> A: [email protected]
> Data: Martedì 19 ottobre 2010, 21:39
> --- On Tue, 19/10/10, sara borelli
> wrote:
> > when using the orginal year variable I have that for
> each
> > state there is a perfect correlation between
> > state dummy, trendstate, trandsquare_state  when
> these
> > are constructed by using the orginal year variable
> >
> > when I look at the correlation between the same
> variables
> > constructed using the rescaled year variable then the
> > correlation is very high but not perfect.
>
> We use the non-linearity of the relationship between a
> variable and its square to identify the parameter for
> each.
> This is another way of saying that the correlation, which
> measures the strength of the linear relationship, must not
> be exactly 1 or -1. However, the function x2 = x^2 is
> almost
> linear in the range 1990 - 2010, which is why you get your
>
> multicolinearity problem, but non-linear in the range 1-20,
>
> which is why you can estimate your model in that case.
>
> Hope this helps,
> Maarten
>
> --------------------------
> Maarten L. Buis
> Institut fuer Soziologie
> Universitaet Tuebingen
> Wilhelmstrasse 36
> 72074 Tuebingen
> Germany
>
> http://www.maartenbuis.nl
> --------------------------
>
>
>
>
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```