data pubexp1; * create data set;

set datpubexp;

y = ee/p;

x = gdp/p;

w = 1/x;

run;

proc sort;

by x;

* part (b) & (d);

proc reg;

model y = x/acov;

output out=pubout p=yhat r=ehat;

proc plot;

plot y*x='y' yhat*x='*'/overlay;

plot ehat*x;

* part (c);

data one;

set pubexp;

if _n_ <= 17;

proc reg;

model y = x;

data two;

set pubexp;

if _n_ >= 18;

proc reg;

model y = x;

* critcal values for tests;

data;

fc = finv(.95,15,15);

tc = tinv(.975,32);

proc print;

* GLS via weighted least squares;

proc reg data=pubexp1;

model y = x;

weight w;

run;