* PS4.4, using DATA4-4, for Table 4.4 and the application in Section 4.6 
read(data4-4) BUSTRAVL FARE GASPRICE INCOME POP DENSITY LANDAREA
* Model A -- the kitchen sink model (unrestricted)
ols BUSTRAVL FARE GASPRICE INCOME POP DENSITY LANDAREA
* save summary statistics for future F-test
genr ESSU=$SSE
genr DFU=$DF
* Model B
ols BUSTRAVL INCOME POP DENSITY 
genr ESSR=$SSE
genr DFR=$df
genr NR=DFR-DFU
* F-test using Model A as unrestricted model and Model D as restricted model
genr Fc=(ESSR-ESSU)*DFU/(ESSU*NR)
sample 1 1
distrib Fc / type=F df1=NR,df2=DFU
sample 1 40
* Model C 
ols BUSTRAVL FARE INCOME POP DENSITY LANDAREA
* Model D
ols BUSTRAVL FARE INCOME POP DENSITY
stop