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RE: st: why reg3 dropped constant term ?


From   KAMAL MANJU <kamaali_1@hotmail.com>
To   statalist-for help STATA <statalist@hsphsun2.harvard.edu>
Subject   RE: st: why reg3 dropped constant term ?
Date   Mon, 3 Jan 2011 00:00:59 +0800

Thank you all for the replies,

I will try the estimation methods you suggested the (2sls and Ivregress) and will share the result.


For you first clarification about the year dummies, Yes, I have excluded y_1 =2000 as usually recommended in dummy variable coding.
I have 8years( 2000-2007) I code them as y_1 =2000 , y_2=2001 ...y_8=2007. In regression I excluded y_1 as base year.

For your last question, regarding my use of the first difference d.cbf and d.rwar. I have the following additional question:

I originally coded the time variable (time trend) as yid (y=year, id= Identifier). In my model when I used this Id= yid as the time or trend variable the constant term is included in reg3 output (not dropped), but when I code the yid as individual year dummies and included the full year dummies -1year (I mean I excluded y_1, and included the remaining y_2 to y_8 in the model) then reg3 will dropped the constant term (with the full 8year-1year dummies).

Note also that when I use only 4years then the constant term is not dropped in the model ( I mean when I split my 8year sample period into 2 4years sub-sample e,g when I use y_2, y_3,y_4, y_5 in this case the constant term is not dropped from reg3 output).

My question is: if there is a collinearity in my model is it between the year dummies and the constant term or with my other variables too? What I should do then in any of this cases?

I hope I am able to explain my problem clearly, I can explain more if necessary.
Thank you all for your valuable answers.

Happy New year.

----------------------------------------
> From: kit.baum@bc.edu
> Subject: re:RE: st: why reg3 dropped constant term ?
> Date: Sun, 2 Jan 2011 08:50:54 -0500
> To: statalist@hsphsun2.harvard.edu
>
> <>
> Here is what I have typed in Stata and the Stata estimated output.
>
> Manually (using hand to type in Stata command window,
>
> reg3 (Leverage: d.lvr=l.lvr d.rwar roa llpta lta liq hhi y_2 y_3 y_4 y_5 y_6 y_7 y_8) (Prisk: d.rwar = l.rwar d.lvr llpta liq lta hhi y_2 y_3 y_4 y_5 y _6 y_7 y_8), small
>
>
> Note that:
> D.cbf and D.rwar are the only two endogenous variables in this model, and that all other variables are considered to be exogenous in this model.
>
>
>
> Try estimating each of these equations via single-equation methods such as -ivregress 2sls- to better diagnose the issues with collinearity. Do y_2-y_8 comprise a complete set of year dummies (or is there an excluded y_1)?
>
> Keep in mind that with each equation estimated with a first difference as the response variable, a constant term would constitute a linear trend coefficient in the level of the response variable. Do you really mean to test for the existence of such a linear trend in levels?
>
> Kit
>
>
>
> Kit Baum | Boston College Economics & DIW Berlin | http://ideas.repec.org/e/pba1.html
> An Introduction to Stata Programming | http://www.stata-press.com/books/isp.html
> An Introduction to Modern Econometrics Using Stata | http://www.stata-press.com/books/imeus.html
>
>
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