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Re: st: RE: RE: estimation with a time trend.


From   natasha agarwal <agarwana2@googlemail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: RE: estimation with a time trend.
Date   Mon, 5 Jul 2010 13:59:38 +0100

On Mon, Jul 5, 2010 at 1:45 PM, natasha agarwal
<agarwana2@googlemail.com> wrote:
> On Mon, Jul 5, 2010 at 1:14 PM, Maarten buis <maartenbuis@yahoo.co.uk> wrote:
>> --- On Mon, 5/7/10, natasha agarwal wrote:
>>> I am afraid I did not understand "year- (or -year-
>>> MINUS> midpoint) for interpretability?"
>>
>> Say you have a variable representing year of birth
>> ranging between 1910 and 1980. I would then usually
>> have a line like this in my do-file:
>>
>> gen c_year = year - 1910
>>
>> Afterwards I would use c_year instead of year. In
>> this case "midpoint" is 1910, and makes sure that
>> your new variable is shifted to the left such that
>> it has the value zero in 1910. This makes sure
>> that the baseline in your models refer to a point
>> at the beginning of your observed period. This is
>> particularly important if you include interactions
>> or if you care about the constant (e.g. in a random
>> effects model)

Can anyone please explain me why is this particularly important if you
include interactions??? and with interactions do you mean interaction
with the time?

Thanks
Natasha


>
>> 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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>>
>

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