Let us compare the fuel efficiency of foreign and domestic cars before and after adjusting for weight. We use gallons per 100 miles (gphm) as our measure of efficiency because it has a more linear relationship with weight.

  unadj adjusted
Car origin
  Foreign -1.005 ** 0.622 **
  (-3.29) (3.11)
Weight (lbs.) 0.002 **
  (13.74)
Intercept 5.318 ** -0.073
  (31.92) (-0.18)
Number of observations 74 74

** p<.01, * p<.05

Foreign cars on average use one gallon less than domestic cars to travel 100 miles, but when we compare cars with the same weight they use 0.62 gallons more.