Solution

Now we want to run:

reg price c.mpg##c.mpg foreign c.weight##c.weight trunk headroom

The coefficient on mpg wasn't signficant before, and neither the coefficient on mpg nor the coefficient on mpg squared are significant now. But to test whether they're jointly significant we need to use the test command:

test mpg c.mpg#c.mpg

The answer is still no.

Last Revised: 12/18/2009