Thursday, April 28, 2011

NFL Draft Pick Value

It's nice to change things up from the NBA playoffs every once in a while, so here's a project that I did over a year ago. It was actually going to develop into my final project for Math of Sports before I got started on the rankings system. This probably would've given much less material to blog about, but that doesn't diminish it's usefulness over the next few days. Below is my chart for average NFL draft pick value.

As a little background, something like this has been bouncing around among NFL teams for years, and they almost all follow the chart. It can produce some shocking results (is the number 1 pick really worth five number 30s?) but trades over the past few years show it's been followed to a T. My graph was supposed to be an improved version of the chart.

To set up my graph I used Career Approximate Value from ProFootballReference.com. It's a rough way to get all players on a statistically equal footing for judging their career quality. While it's not perfect, its definitely good enough to get a rough number for value, great players have up over 100 while crap players can have CarAV in the single digits. I took the data for the top 60 draft picks in the 1970s, and the top 30 in the 1980s (people who's career had finished. Also, I typed this all in because I didn't think of copy paste. Dumb.). After doing some moving averages, I decided the best fit was an exponential, which is also fitted on the graph.

As you can see, things drop off fairly slowly. The "half-life" (physics!) is about 38 draft picks, meaning that one pick is worth about two picks from a little over a round later. The draft chart actually follows this pretty well from the mid-4th to mid-7th rounds, but overestimates the value of high picks at other times. The exponential fit may slightly underestimate the value for the top few picks, but just by a little bit. It's clear though that the number one pick should probably be worth 2 number 30s, not 5.
Also amusing to note is the bizarre curse of pick 7. Over the 20 years of data here it's averaged being worth that of a pick 20 spots lower. Adrian Peterson and Champ Bailey have probably reversed that recently, but it's still maybe worth a though for the 49ers and their new coach Harbaugh.
On the whole, this graph shows us that the draft chart used by NFL teams significantly overvalues top picks. So if you're team trades some picks to move up in the draft this weekend you should be worried about the deal you're getting. If they play it smart and move down however, it means somebody might be reading Kobe, Tell Me How My Stats Taste.

p.s. The third ESPN article went up a couple days ago. It may turn into a playoff long gig. Fingers crossed.
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