NFL: QBs worth more than RBs, but RBs contribute faster

Elite quarterbacks in the NFL are scarce. Teams with high first-round draft picks are licking their chops dreaming of Terry BridgewaterJohnny Manziel and Blake Bortles. Teams with lower draft picks have to weigh the value of drafting a young promising quarterback versus veterans who are "more-known quantities," but out-of-favor. In addition, when considering draft picks, trades and free agency, teams need to study the overall impact on their team — weighing player potential and team needs.

I recently studied a sampling of above-average veteran NFL quarterbacks. Our group includes veterans such as the Manning brothers, Tom BradyDrew Brees and Michael Vick. We learned the following:

The average annual quarterback rating in our sample is 91.3.

Variability of performance — within each player's career — is higher than we expected. Annual performance varies about 12 percent, defined as standard deviation as a function of each player's average QB rating.

The average QB rating during the first full two seasons of the quarterbacks' careers is 71.1. This represents just 78 percent of the average 91.3 career QB rating.

A large majority of quality quarterbacks take at least a few years to fully develop. It takes time for quarterbacks to get used to the speed and level of the NFL.

Tom Brady had one of the best career starts relative to his career average. Even so, his QB rating of 86 during his first full two seasons represents just 90 percent of his career QB rating of 95.7.

As a comparison, we reviewed another important position: running back. While the passing game has taken the upper hand from the running game in today's NFL, the data shows some interesting results.

Running backs offer less variability than quarterbacks. In our sampling of quality veteran running backs, performance variability as a function of individual performance is 10 percent (compared to 12 percent for quarterbacks).

Perhaps more importantly — and very interesting — the average running back in our sample was able to achieve 104 percent of his average output during his first full two seasons (compared to 78 percent for quarterbacks).

On average, running backs are able to contribute to their teams almost immediately.  There is something to be said about fresh, young legs.