Dear Statlist users,

I am using Stata 14.1.

I am trying to estimate wage inequality (by Gini coefficient) by different fields of graduation between 2009 and 2017.

The following two commands yield the same Gini coefficients where group_yearfield is a grouping variable that combines year and field.

ineqdeco wage_real , by(group_yearfield)
Subgroup indices: GE_k(a) and Gini_k
group(year field_isced_agg) GE(-1) GE(0) GE(1) GE(2) Gini
2009 Education sciences 0.02628 0.02516 0.02463 0.02462 0.12507
2009 Arts, Humanities & Languages 0.23779 0.13729 0.09504 0.07554 0.20667
2009 Social sciences and journalism 0.32876 0.20835 0.16636 0.15805 0.31587
2009 Business Administration & Law 0.23097 0.16740 0.14945 0.15863 0.29832
2009 Environment sc, math. & stat. 0.10441 0.08880 0.08085 0.07810 0.22543
2009 ICT 0.00000 0.00000 0.00000 0.00000 0.00000
2009 Engineering, Manufacturing & Arc 0.18252 0.14354 0.12618 0.12286 0.27576
2009 Agriculture & veterinary 0.12320 0.11102 0.10803 0.11267 0.25732
2009 Health & Welfare 0.10245 0.09145 0.08861 0.09267 0.23524
2009 Services 0.20181 0.15249 0.12777 0.11659 0.26928
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ginidesc wage_real , by(group_yearfield)

K Gini_k
2009 Education sciences 0.125
2009 Arts, Humanities & Languages 0.207
2009 Social sciences and journalism 0.316
2009 Business Administration & Law 0.298
2009 Environment sc, math. & stat. 0.225
2009 ICT 0.000
2009 Engineering, Manufacturing & Arc 0.276
2009 Agriculture & veterinary 0.257
2009 Health & Welfare 0.235
2009 Services 0.269
Then I want to decompose wage inequality separately for each year and I type the commands

ineqdeco wage_real if year==2009 , by(field)
ginidesc wage_real if year==2009 , by(field)

Here, the Gini coefficients by field with ineqdeco are the same with the above results

ineqdeco wage_real if year==2009 , by(field)
Education sciences 0.02628 0.02516 0.02463 0.02462 0.12507
Arts, Humanities & Languages 0.23779 0.13729 0.09504 0.07554 0.20667
Social sciences and journalism 0.32876 0.20835 0.16636 0.15805 0.31587
Business Administration & Law 0.23097 0.16740 0.14945 0.15863 0.29832
Environment sc, math. & stat. 0.10441 0.08880 0.08085 0.07810 0.22543
ICT 0.00000 0.00000 0.00000 0.00000 0.00000
Engineering, Manufacturing & Architectur 0.18252 0.14354 0.12618 0.12286 0.27576
Agriculture & veterinary 0.12320 0.11102 0.10803 0.11267 0.25732
Health & Welfare 0.10245 0.09145 0.08861 0.09267 0.23524
Services 0.20181 0.15249 0.12777 0.11659 0.26928

However, the Gini coefficients with ginidesc are different with the Gini coefficients I got above for 2009.

ginidesc wage_real if year==2009 , by(field)
Education sciences 0.235
Arts, Humanities & Languages 0.298
Social sciences and journalism 0.125
Business Administration & Law 0.269
Environment sc, math. & stat. 0.225
ICT 0.000
Engineering, Manufacturing & Architectur 0.276
Agriculture & veterinary 0.257
Health & Welfare 0.316
Services 0.207
What happens to the ginidec command when I use the if qualifier?

Many thanks in advance.
Elif.