More efficient football coaches?

If they listened to David Romer, football coaches would probably be better off.

Addendum:

Apparently Romer is silly and used third down numbers instead of fourth down numbers for his statistics. This was a major error and severely compromises his study. That said, coaches are still far too conservative! They still probably shouldn't go for it on 4th and 2 from their own 10, but the 50-yard-line would be a different story...