When ESPN's Sports Analytics Team rebuilt its expected points model in the offseason, one of the new features that was built in was the ability to adjust the expected points added (EPA) values based on the type of play that was called. This means we can fairly compare the results of plays against similar plays -- that is to compare run plays to other run plays, and not against passing plays. This adjustment is useful when comparing team running games to each other.
Teams almost universally run too often, which generally makes running plays have negative EPA.