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Stata Technical Bulletin

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gp(gpname) creates a new categorical variable, gpname, containing categories summarizing group membership.

Example

To produce output mimicking the UK official low income statistics, we use the mean income as the cut-off value input into
xfrac:

. summarize eybhc [fw=wgt]

Variable Obs        Mean Std. Dev.       Min        Max

---------+-----------------------------------------------------

eybhc I 5.6e÷07    233.0179   199.0178 -123.9898   7740.044

. local mean = .result(3)
. xfrac eybhc [fw=wgt], cut('meanz) gp(fracgp)

Warning: eybhc has 20 values < 0. Used in calculations
Proportions of the sample in subgroups defined
by values of eybhc between specified fractions
of a cut-off value = 233.01790

Fractions of
cut-off      I

Freq.

Percent

Cum.

<.1 I

4ББ1Б2

0.81

0.81

.1-.2 I

482238

0.86

1.68

.2-.3 I

912Б26

1.63

3.31

.3-.4 I

3983433

7.13

10.44

.4-.5 I

ББ02971

9.8Б

20.30

.5-.6 I

Б186Б97

9.29

29. Б8

.6-.7 I

493ББ14

8.84

38.42

.7-.8 I

4777040

8.ББ

46.97

.8-.9 I

4341904

7.77

Б4.7Б

.9-1.0 I

4364218

7.81

62. Б6

1.0-1.1 I

3234833

Б.79

68. ЗБ

1.1-1.2 I

2678779

4.80

73.1Б

1.2-1.3 I

26БББ24

4.7Б

77.90

1.3-1.4 I

209Б389

3.7Б

81.66

1.4-1.5 I

1683166

3.01

84.67

1.5-1.75 I

3149798

Б.64

90.31

1.75-2.0 I

1848821

3.31

93.62

2.0-2.5 I

19020Б9

3.41

97.02

2.5-3.0 I

721933

1.29

98.32

>=3.0 I

939810

1.68

100.00

—— — ——— — ——— —-⅛--

Total I

ББ8Б170Б

100.00

There is no official poverty line in Britain, but half of the average income is used by many commentators as such a threshold.
The xfrac output shows that about one fifth of the UK population in 1991 had incomes below one half of contemporary mean
income (and 62.6% had incomes below the mean). But observe too that 38% of the population have incomes between 40%
and 60% of mean income. Thus relatively small changes in the threshold defining the poverty line can have a large impact on
estimates of the proportion who are “poor”.

The command above also created a new variable summarizing income group membership. If we were now to type
. table fracgp tenure [fw=wgt], row col

we could compare the shape of the income distribution across housing tenure groups.

ineqdeco, ineqdec0: inequality indices, with decompositions by population subgroup

ineqdeco and ineqdecθ estimate a range of inequality and related indices commonly used by economists, plus decom-
positions of a subset of these indices by population subgroup into within- and between-group inequality components. Inequality
decompositions by subgroup are useful for providing inequality profiles at a point in time, and for analyzing secular trends using
shift-share analysis. Unit record (micro level) data are required. For a non-technical introduction to the topic, see Jenkins (1991).
Standard textbook treatments are provided by Cowell (1995) and Lambert (1993).

Inequality indices estimated by ineqdeco are: members of the single parameter Generalized Entropy class GE(α) for
a = -1,0,1,2; the Atkinson class A(e) for e = 0.5,1,2; the Gini coefficient, and percentile ratios such as p90∕p10 and
p75∕p25. Also presented are related summary statistics such as subgroup means and population shares. Optionally presented are



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