They are nothing but averages across a game.
I could be 8-8, pass 600 yards in our 8 wins and 200 yards in our 8 losses in the same amount of series per game. Yet, our averages across the whole season are nothing short of spectacular, ranking us 5th. But supposedly our offense is all world, even though eight games, we absolutely blew. Then there is the issue of blow-outs. We could score 14 pts in two games in the fourth quarter, like we did in blow-outs against the Bears and Saints, when the defenses were playing soft. That would boost our 'passing efficiency' rating enough to up our rank by scores per drive say .3, which is significant according to that measurement and jump us up a few rankings. And further if you look at the number .3 as an average, saying you get a total of 10 drives, that is a single field goal per every ten drives. Is that telling us much in the scheme of the judgement of an offense in a particular game?