The datafile contains 1991 season leading quarterback and total team salary
for football teams in the American Football Conference (AFC) and National
Football Conference (NFC) of the National Football League(NFL). Two poten-
tial influential observations (Steelers and Bears) are present. They are the 
high X-observations in the scatter diagram shown below. The student should
try the regression with and without these teams to see if their inclusion or ex-
clusion makes a material difference. 

The two conferences are distinguished in the scatter diagram. The student 
should test if the same regression (average level and slope) applies equally
to the two conferences.