*! version 1.1.0 24may2010

help nopomatch

Title

nopomatch -- Decomposition of Nopo (2008)

Syntax

nopomatch
matchvar
[matchvar(s)]
[if]
,
outcome(varname)
by(varname)
[options]

Parameters

matchvar(s): list of variables used to match observations of the groups defined by by().

outcome: outcome for which the gap will be computed. (e.g.: wage)

by: dummy (0/1) that discriminates the sample to perform the computation of the gap. (e.g.: gender).

Main
sd computes standard error.

replace deletes the _match and _supp variables previously created (if any).

reportby(varname) split the results for different groups of observations.

fact(factor-variable) specifies the use of frequency weights.

filename(file-name) saves output in STATA file.

Description

nopomatch -- module to decompose the gap in an outcome between two groups using matching, following the methodology developed by Nopo (2008). nopomatch performs the matching,
computes the gap decomposition and provides the standard error of the unexplained component of the gap.

Options

Main

sd computes standard error of the unexplained components of the gap. Note that the usage of this option substancially increases significantly
the computation time.

replace deletes the _match and _supp variables previously created (if any).

reportby(varname) repeats the command for each group of observations of each category of varname.

fact(varname) specifies the use of a weighting factor variable (frequency weight) in the data.

filename(string) creates an output STATA file (string.dta) with the results of the decomposition.

Output

A typical output of the nopomatch module looks like this:

****************************************************
***** Gap in matchvar(s) decomposition
****************************************************

D = # is the total gap, the difference between averages in the outcome-variable of the comparing groups. It is
expressed as a percentage of the average of outcome-variable for the group in which by-variable=0

D0= # is the unexplained part of the gap.

DM= # is the part of the gap that can be explained by the differences in characteristics between
two groups of the individuals with by-variable=1, that are in and out of the common support of the variables defined by match-variable(s)

DF= # is the part of the gap that can be explained by the differences in characteristics between
two groups of the individuals with by-variable=0, that are in and out of the common support of the variables defined by match-variable(s)

DX= # is the part of the gap that can be explained by differences in the distribution of characteristics
of the two groups discriminated by by-variable in the common support of the variables defined by match-variable(s)

****************************************************
percM= # is the percentage of the individuals with by-variable=1 that are in the common support of the variables defined by match-variable(s)

percF= # is the percentage of the individuals with by-variable=0 that are in the common support of the variables defined by match-variable(s)

****************************************************

Note that D = DO + DM + DF + DX. For technical details see Nopo (2008).

Examples

. nopomatch age education, outcome(wage) by(male)

. nopomatch age education, outcome(wage) by(male) fact(freqweight) sd replace filename(example1)

. nopomatch age education occupation sector, outcome(wage) by(male) fact(freqweight) reportby(education)

. nopomatch age education occupation sector, outcome(wage) by(male) sd replace fact(freqweight) reportby(firmsize) filename(example2)

References

Nopo, H. 2008. Matching as a Tool to Decompose Wage Gaps Review of Economics and Statistics, 90(2): 290-299.

Acknowledgements

This code was built from previous versions developed by Sebastian Calónico and Luana Marques.

Disclaimer

This program is provided without warranty of any kind. The authors are not responsible for any cost derived by the usage of this program.

Authors

Atal, Juan Pablo; Hoyos, Alejandro and Hugo Nopo. If you observe any problems mailto:hugon@iadb.org