Here's another good resource related to this topic:
http://www.sportingcharts.com/nfl/stats/drops/2013/
It tracks WR receptions, drops, and targets. Last year, Pierre Garcon and Andre Johnson led the league with 181 targets. Pierre Garcon caught 113 of those passes and dropped 7; Andre Johnson caught 108 and dropped 8. Since drops only caught the balls that hit the receiver's hand but he didn't catch, it can be assumed that the 61 passes thrown to Pierre Garcon were completely out of reach, reflecting the quarterback's accuracy. That means that one of out every three passes thrown his way were inaccurate.