(* PS4.4, using DATA4-4, for Table 4.4 and the application in Section 4.6 *)
ols BUSTRAVL 0 FARE GASPRICE INCOME POP DENSITY LANDAREA ;
(* omit variables -- Model B *) 
omit GASPRICE LANDAREA FARE 
(* estimate full model and omit variables one at a time *)
ols BUSTRAVL 0 FARE GASPRICE INCOME POP DENSITY LANDAREA 
(* Model C *)
omit GASPRICE
(* Model D *)
omit LANDAREA
