In 2016, Sam Bradford set a single-season NFL record for completion percentage (71.6 percent) but finished 17th in Total QBR. Clearly, completion percentage can be a misleading stat, boosted by short passes that don't lead to successful plays for an offense.
Football Outsiders has used game-charting data to create a better way of quantifying accuracy and completion percentage. The core idea is passing plus-minus, which estimates how many passes a quarterback completed compared to what an average quarterback would have completed based on each throw's distance, the yards needed for a first down, and which side of the field the pass was thrown to.