(* PS4.3, using DATA4-3, for Examples 4.12 and 4.13 in Section 4.5 *)
ols housing 0 gnp intrate 
(* Model B in Example 4.12 *)
omit intrate
(* Model C in Example 4.13 *)
ols housing 0 gnp intrate pop unemp
(* Wald test for omitting pop and unemp *)
omit pop unemp 
(* add unemp back for Practice Problem 4.8 *)
add unemp 
