http://www.footballoutsiders.com/fei-ratings/2014/fei-week-3

"How valuable is a possession that starts at the opponent’s 4-yard line? From 2007 to 2012, there were 79 total drives in FBS vs. FBS games in which an offense started a drive from that position on the field. The offenses scored 60 touchdowns on those drives (75.9 percent). Four of those drives resulted in a turnover, one on a turnover on downs, and three resulted in time running out at the end of a half. The other 11 resulted in a field-goal attempt, nine of which were successful. The field-position value of the opponent’s 4-yard line is 5.8 points, according to my data."