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From |
Kit Baum <baum@bc.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Re: dummy question |

Date |
Mon, 29 Nov 2004 08:40:47 -0500 |

An approximate solution to this question (as a little algebra will show) is to define the dummies 1-(G-1) as d_i - d_G for G groups. (Approximate depending on how group sizes differ across the dummies). As an example:

webuse grunfeld, clear

drop if company>5

tab company, gen(co)

forv i=1/4 {

gen Co`i' = co`i'-co5

su invest

reg invest co1-co4

reg invest Co*

lincom -1*(Co1+Co2+Co3+Co4)

As you can see, the constant term in the latter regression is the grand mean.

The coefficient on the excluded dummy can be expressed (via lincom) as minus the sum of the other dummy coefficients.

Kit Baum, Boston College Economics

http://ideas.repec.org/e/pba1.html

On Nov 29, 2004, at 2:33 AM, Javier wrote:

One possibility recommended in the literature was to use restricted least squres method (Greene, Seaks 1991). It recommends to set the restrictions to dummies so that the weighted (according to weights of observation in endogenous variable) sum of all dummies (no reference category is omitted) is equal to zero.

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