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Re: st: Including constant?


From   Nils Braakmann <nilsbraakmann@googlemail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Including constant?
Date   Thu, 2 Jun 2011 06:31:44 +0100

Interesting to learn about these disciplinary differences. In
economics the most common thing nowadays seems to be to only report
coefficients/results for your main variable of interest, omit results
for control variables, constants etc.  and just mention that these
were included somewhere in the text/a table footnote.

Cheers,
Nils

On Wed, Jun 1, 2011 at 5:28 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> In various Earth and environmental sciences in which I write or review papers leaving out the constant would be generally regarded as gross statistical illiteracy.
>
> Nick
> n.j.cox@durham.ac.uk
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Richard Williams
>
> At 07:23 AM 6/1/2011, lreine ycenna wrote:
>>Do we typically not have to include constants in regression tables
>>when presenting them?
>
> You can probably say most or all of what you want to say without
> including the constant. After all, how many times do you see a paper
> discussing the values of the constants?
>
> But, I personally always include them. It is particularly useful if
> somebody wants to calculate a yhat value for some combination of
> values for the Xs. How useful the constant is as a standalone value
> depends on the coding of the Xs. The constant is the value someone
> would have if they had a value of 0 for every X. Often such a person
> cannot exist because one or more variables cannot take on a value of
> 0, e.g. nobody has 0 height, and nobody gets a score of 0 on a test
> scaled to range between 400 and 1600. However, if you center the Xs
> (subtract the mean from each case for each X) then the constant
> becomes the predicted score for a person who has average values on
> every X. Such a person (or someone close to it) may actually exist,
> making the constant more interpretable as a stand-alone number, i.e.
> the constant is the score a totally average person would be expected
> to have. Or, if the model just has dummy variables (female, black)
> then the constant could be the average score for, say, a male white.
>
>
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