This article is part of our The Stats Room series.
Football is a tough sport with most players only lasting in the league a short time. In this brutal game, how long can players last before they begin to fall apart? Is the decline slow and steady or an immediate drop? Let's examine how football players' production changes as they age.
Teams have taken player decline into account for years, lowering the value placed on drafting running backs, especially. With the grind of years of defenses hitting them, running backs come to the league possibly broken already. Then as they break down, they are quickly replaced with a younger, faster, cheaper model.
Wide receivers, on the other hand, come into the league with a large learning curve. The quarterback and receiver must get on the same page for timing routes for those perfect passes. This learning takes time. Additionally, wide receivers don't take the constant pounding running backs endure with every gang tackle.
To find how these players age, I will use a process of determining aging curves that I used with baseball players called the delta method (detailed link).
The aging curve was created by the delta method by chances using their harmonic means. With this method, there's a small survivor bias summarized by Mitchel Lichtman at the Hardball Times:
… survivor bias, an inherent defect in the delta method, which is that the pool of players who see the light of day at the end of a season (and live to play another day