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Parameter estimate for dummy variable

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New Contributor
Posts: 4

Parameter estimate for dummy variable

Hi,

 

The DATA is attached.

 

I am trying to find the effect from Industry (dummy) on the Tobin variable with a random effect model, but when I do the regression with all 6 industry-dummies the dummy for the industry 'Industrials' gets a 0 parameter estimate. When I exclude one industry-dummy (not Industrials) the dummy for Industrials gets a parameter estimate.

 

Could anyone tell me why this happen? Smiley Happy

 

 

 

 

 

Super User
Posts: 18,603

Re: Parameter estimate for dummy variable

That's how dummy values work. 

If you have n levels you n-1 parameters since the last option is all other parameters set to 0. 

The term for what your seeing is called overparametization. 

Here's a quick overview and refer to a statistics textbook for more details. 

 

http://www.ats.ucla.edu/stat/mult_pkg/faq/general/dummy.htm

 

New Contributor
Posts: 4

Re: Parameter estimate for dummy variable

Thank you for your answer.

So the industrials-dummy is the base level.is it somehow possible to get a table where all estimates of the dummy variables are shown, and not the level compared to the base dummy variable industrials?
New Contributor
Posts: 4

Re: Parameter estimate for dummy variable

I would like the results to be like this, so it is possible to interpret the results on how sectors influence.

 

Untitled.jpg

Super User
Posts: 18,603

Re: Parameter estimate for dummy variable

You have to have a reference level so no. One will have to be missing. You can decide which.
New Contributor
Posts: 4

Re: Parameter estimate for dummy variable

[ Edited ]

How do I find the influence from the excluded variable? 

 

I would like to interpret how each sector influence on Tobin and not to the difference between the sector and the reference level. 

Is it the effect coding method I should use? And is that possible with random effect model? Or should I just run regression without the intercept and interpret the results?

 

Valued Guide
Valued Guide
Posts: 684

Re: Parameter estimate for dummy variable

With the standard GLM parameterization, the intercept is the last level of the factor (level 6 in your case). You can take out the intercept (noint) and the six levels have estimates, with a direct interpretation. That is fine. However, the type III test for the factor is not testing the equality of the parameters (it is now testing the equality of the parateters all to 0). That is a big difference.

 

Using the default parameterization, you can use estimate statements to get the estimates for each level of the factor. Generic example:

estimate '1' int 1 f 1 0 0 0 0 0;

estimate '2' int 1 f 0 1 0 0 0 0;

and so on. Here "f" is my generic name for your factor.

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