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Re: st: conception confusion - "fixed effects" and time effect on data with time factor


From   House Wang <jwanghouse@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: conception confusion - "fixed effects" and time effect on data with time factor
Date   Fri, 21 Oct 2011 15:56:37 -0500

I think I have learned something from your response. "models are
supposed to be useful, not true." This is the most important of the
discussion. Thank you very much.
For the model, I want to measure the maturity of an institution in
manipulating rules, which are supposed to increase across years.
Proximately, it is like a kid grow up. This is why I use year as a
trend variable.

On Fri, Oct 21, 2011 at 12:37 PM, Maarten Buis <maartenlbuis@gmail.com> wrote:
> On Fri, Oct 21, 2011 at 6:58 PM, House Wang <jwanghouse@gmail.com> wrote:
>>
>
> You are right to be skeptical, so am I. Your model identifies the
> difference between "trend time" and "proxy time" using the assumption
> that the trend is linear, which is almost never true. You really need
> to decide what it is that you want to measure, and and think of a
> model that will get you that. From that, derive the role time plays in
> your model (note model, not data or reality or ...). By focusing on
> what you want to know, you can often trim your model to manageable
> proportions. If you try to represent "reality" your model tends to
> explode. In the end: models are supposed to be useful, not true.
>
> 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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