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st: multiple lorenz curves with glcurve


From   "Reza Daniels" <Reza.Daniels@uct.ac.za>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: multiple lorenz curves with glcurve
Date   Mon, 27 Aug 2007 12:02:04 +0200

Dear Statalisters,


I am setting an undergraduate assignment for development economics that uses Microsoft Excel to compute poverty lines and draw lorenz curves. I would like to do the same using Stata, but I'm having trouble with -glcurve- when I try and simultaneously graph three separate measures for income. Here is the code I've used:


*** BEGIN CODE ***

clear
cd "C:\Documents and Settings\Administrator\My Documents\Teaching\2007\eco2008s"
log using "assgt1.smcl",replace
version 8.2
set more off

set obs 30
gen obsno=_n
gen gender=.		
replace gender=1 in 1/15
replace gender=2 in 16/30

set seed 135791113
gen z1=9+invnorm(uniform())		
gen income=round(exp(z1))

di 365*7		/* 2555 = World Bank annual $1/day povline in local currency */
di 800*12		/* 9600 - SA Treasury monthly povline */

povdeco income,pl(2555)		/* Poverty */
povdeco income,pl(9600)
sumdist income
inequal income

gen inc2=1200+income	/* Basic income grant */
povdeco inc2,pl(9600)
sumdist inc2
inequal inc2

gen inc3=.			/* Progressive income tax */
su income,det
replace inc3=income*0.9 if income<=r(p25)
replace inc3=income*0.8 if income>r(p25) & income<=r(p50)
replace inc3=income*0.7 if income>r(p50) & income<=r(p75)
replace inc3=income*0.6 if income>r(p75)
povdeco inc3,pl(2555)
povdeco inc3,pl(9600)

** BREAK ***


Now I'd like to compare the three Lorenz Curves for income, inc2  & inc3. I'm using the following code:


* CODE STARTS AGAIN ***

glcurve income,gl(g1) p(p1) nograph
glcurve inc2,gl(g2) p(p2) nograph
glcurve inc3,gl(g3) p(p3) nograph
twoway (line g1 p1) (line g2 p2) (line g3 p3) 

*** END CODE ***


When I use this code, I get the cumulative population on the x-axis but it looks like I'm getting actual income (rather than cumulative) on the y-axis. 


My question is: (1) How do I change this to plot the three measures simulataneously? (2) How do I include the 45 degree line on the graph?


Many thanks,
Reza



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