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st: Problem with excluded observations with -ginidesc-

From   Joe McCrary <>
To   Statalist <>,, Amanda Hoffman <>
Subject   st: Problem with excluded observations with -ginidesc-
Date   Tue, 14 Sep 2010 10:19:26 -0400

Hi all.

I've been using -ginidesc- to develop inequality indices of
school-level measures for several districts in the U.S. My goal is to
be able to chart them longitudinally to see if enrollment policies
impacted the mixes of students (e.g., those eligible for free and
reduced-price meals (FRL)).

In 2003, one of the states did not report FRL data, so I wrote in a
statement to exclude those observations for that year:

. ginidesc  Pfrl03 if DistID~=3700720, by(DistID)

Gini Coefficient by subgroups
of DistID

        K |     Gini_k
   625690 |      0.337
  1201710 |      0.225
  3700720 |      0.274
Stored in matrix

As you can see, even though I was excluding District 3700720, ginidesc
still reported results for it. Also, the numbers for the other
districts were way out of line with the years before and after 2003.
So since -ginidesc- calls -ineqdeco-, I then ran that to compute the
gini indices, which produced a table that makes more sense:

. ineqdeco Pfrl03 if DistID~=3700720, by(DistID)

Subgroup indices: GE_k(a) and Gini_k

   DistID |     GE(-1)       GE(0)       GE(1)       GE(2)        Gini
   625690 |    0.82561     0.24858     0.15316     0.14355     0.27361
  1201710 |    0.32468     0.21598     0.18285     0.18375     0.33745
  2503270 |    0.09620     0.08651     0.08126     0.07955     0.22489
  3700720 |
 The Gini coefficients are consistent with those in the other years,
and 3700720 is excluded.

Anyone using -ginidesc- with subgroups, especially when there are
cases that are being excluded, should carefully check their results
against -ineqdeco-.

Joe McCrary
Senior Research Associate
260 Peachtree St., Suite 2200
Atlanta, GA 30303

ph: 541-782-8626
fax: 404-393-3797

Skype: joe.mccrary
Google talk; joe.mccrary

"No problem can be solved from the same level of consciousness that created it."
--Albert Einstein
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