st: Re: Time invariant variables and panel data

["Christer Thrane" <ch-thran@online.no>]

Hi,

If you estimate random effects models, you can have both time-varying and 
time-invariant variables on the right hand side.

If you estimate fixed effects models, you must have time-varying on the 
right hand side. But fixed effects also handles interactions between 
time-varying and time-invariant right hand side variables. (Then the 
interaction is no longer time-invariant.)

Take a look at Woldridge's Basic Econometrics. A modern introduction--it's 
on Stata website.

HTH

Christer
************************************************
Professor Christer Thrane
Department of Social Science
Lillehammer University College
2626 Lillehammer, Norway
+ 47 61 28 81 70 (fax)
+ 47 61 28 82 47 (phone, work)
+ 47 61 25 53 04 (phone, home)
E-mail, work: christer.thrane@hil.no
E-mail, home: ch-thran@online.no
************************************************



----- Original Message ----- 
From: "Rho YH" <mania1@korea.ac.kr>
To: <statalist@hsphsun2.harvard.edu>
Sent: Saturday, May 27, 2006 4:48 PM
Subject: st: Time invariant variables and panel data



> I have incidentally found that panel data models (as far as I found the 
> Statalist, xtreg with -FE option)
> cannot have time invariant variables and will be automatically omitted 
> when included.
> In a general sense, then all xt- models (including xtgee) cannot have time 
> invariant variables?
> Or in what instance does this fact come in effect?
> Second, then does this mean that I cannot use time invariant variables 
> (like sex (M/F)) even
> when these variables may be important?
> I have two books about panel data (Twisk, and Sophia Rabe-Hesketh) but did 
> not find this fact.
> Is it written in these books?

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