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

 From House Wang To statalist@hsphsun2.harvard.edu Subject Re: st: conception confusion - "fixed effects" and time effect on data with time factor Date Tue, 18 Oct 2011 12:58:53 -0500

```Maarten,

Thank you very much for your insights.
I think you are right that this is a cross-sectional data, not a panel data.
The next step, then, is to test the effect of year as a regular
variable on the data.
Period is definitely a right time axis, because I am talking about
years (or even Congress - every two years).
In this study, I am interested in the random effects of the year
variable, which means the errors of D.V. due to year.
To measure the random effects of year variable, the correct STATA
command is to add i.year to the model, right?
(There is no age or cohert in my data).
Thanks.

Jianying

On Tue, Oct 18, 2011 at 2:13 AM, Maarten Buis <maartenlbuis@gmail.com> wrote:
> On Tue, Oct 18, 2011 at 3:15 AM, House Wang wrote:
>> Yes, the data is like survey done across 30 years, each time with same
>> measures, but on different persons.
>> How could I understand time effect on this kind of data? Is there fixed
>> effects on them? and how to test them?
>
> You just have cross-sectional data, so forget the comparison with
> panel data. Time is just a regular variable like any other, and it
> measures the period at which the interview took place. This can be
> relevant when you want to analyze questions that are explicitly or
> implicitly referring to "now". However, you need to decide whether
> period is the right time axis. A common alternative is cohort, i.e.
> year of birth. Also note that you cannot include age, period and
> cohort in your model as they will be perfectly collinear: cohort =
> period - age.
>
> 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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```