//cd /netscr/khrapov/stata/rec02
clear
use zismall

reg idealnum ageyr educf
reg idealnum ageyr educf if city==1
reg idealnum ageyr educf if commune==1
reg idealnum ageyr educf if confarm==1

g ageyr1=ageyr*city
g ageyr2=ageyr*commune
g ageyr3=ageyr*confarm
g educf1=educf*city
g educf2=educf*commune
g educf3=educf*confarm

reg idealnum ageyr1 ageyr2 ageyr3 educf1 educf2 educf3

test ageyr1=ageyr2=ageyr3
test educf1=educf2=educf3

// joint test
test (educf1=educf2=educf3) (ageyr1=ageyr2=ageyr3)

// test in two lines
test educf1=educf2=educf3, notest
test ageyr1=ageyr2=ageyr3, accum

reg idealnum city commune confarm ageyr1 ageyr2 ageyr3 educf1 educf2 educf3, noconst

// test all coefficients, including constant
test (city=commune=confarm) (educf1=educf2=educf3) (ageyr1=ageyr2=ageyr3)
test ageyr1=ageyr2
test ageyr1=ageyr3

// compare t-stats. more efficient
reg idealnum ageyr educf if city==1
reg idealnum ageyr educf 

tabulate idealnum
histogram idealnum
kdensity idealnum

g age2=ageyr^2
g educ2=educf^2
g age_educ=ageyr*educf

reg idealnum ageyr educf age2 educ2 age_educ