When I went on the Advanced NFL Stats Podcast in late December, I discussed my use of Z-scores to measure the Seattle pass defense. Host Dave Collins asked me if I was planning on using Z-scores to measure other things, like say, Adrian Peterson’s 2012 season. I told him that would be an interesting idea to look at in the off-season.

Well, it’s the off-season. So here’s what I did.

1) For every season since 1932, I recorded the number of rushing yards for the leading rusher for each team in each league. So for the Minnesota Vikings in 2012, this was 2,097.

2) Next, I calculated the average number of rushing yards of the top rusher of each other team in the NFL. In 2012, the leading rusher on the other 31 teams averaged 974 yards.

3) Then, I calculated the standard deviation of the leading rushers for all teams in the NFL. In 2012, that was 386 yards.

4) Finally, I calculated the Z-score. This is simply the difference between the player’s average and the league average (for Peterson, that’s 1,123), divided by the standard deviation. Peterson’s Z-score was 2.91, good enough for 15th best since 1932. The table below shows the top 250 seasons using this method from 1932 to 2013; it’s fully searchable and sortable, and you can change the number of entries shown by using the dropdown box on the left. [continue reading…]