???--------------------------------------
??? Problem Set No. 1: Repetition OLS
??? by: Katrin Sommerfeld
???--------------------------------------

options crt;
freq N;

? Read in the data
? Adjust the location of data file if necessary
read (file='L:\Microeconometrics\earnings04.raw')	sex age educ exper noschool medschool highschool notrain appren uni earn ;

? Descriptive Statistics and checking
?--------------------------------------
msd(terse) @all ;
?stop;	

  
?-------------------------------------------------------------
? Exercise 1
?-------------------------------------------------------------
title 'Exercise 1';
olsq earn c educ exper;
?stop;


?-------------------------------------------------------------
? Exercise 2
?-------------------------------------------------------------
? Exercise 2a
title 'Exercise 2a: Dummy';
olsq earn c educ exper sex ;
?stop


? Exercise 2b
title 'Exercise 3b: Interaction Dummy'; ? Here: "Slopedummy"
genr educsex=educ*sex ;
olsq earn c educ exper sex educsex ;
?stop;


? Exercise 2c
title 'Exercise 3c: Dummies';
olsq earn c exper sex appren uni ;

title 'Hypothesis test for joint influence of training degrees';
frml test1 appren ;
frml test2 uni	;
analyz(noconstr) test1 test2 ;

?stop;

?-------------------------------------------------------------
? Exercise 3
?-------------------------------------------------------------

title 'Exercise 3a: quadratic Specification';

genr exper2  = exper**2;

olsq earn c educ exper exper2 sex ;
?stop;

frml test3 exper  ;
frml test4 exper2 ;
 
title 'Test for joint significance of both experience terms';
analyz(noconstr) test3 test4;
?stop;


title 'Exercise 3b';
? marginal effect of work experience in quadratic specification
? Partial derivative of earnings on experience:
? d earnings/d exper=@coef(3) + 2*@coef(4)*exper 

set cexper=@coef(3); print cexper;
set cexper2=2*@coef(4); print cexper2;

title 'Earnings gain after one year on the job';
set earn1=cexper + cexper2*1; print earn1;

title 'Earnings gain after ten years of work experience';
set earn10=cexper + cexper2*10; print earn10;

?stop;

?-----------------------------------------------------
? Supplementary exercise 4
?-----------------------------------------------------
title 'Exercise 4: semilog model';

genr lnearn=log(earn);
msd(terse) lnearn earn;
olsq lnearn c educ exper exper2 sex ;


end;