Home Cookin' - How NFL Stat Crews Affect IDP, Pt. 3

In part one and two of this series I showed that there's significant evidence of bias between NFL stat crews when scoring solo tackles and assists. The third unofficial defensive statistic is passes defensed. In the conclusion to this series I'll discuss the results of the five- and 10-year comparative studies on PDs and summarize the big picture strategy to take advantage of this home cookin' in IDP fantasy football leagues.

I was able to draw three conclusions from the passes defensed results. First, between the 2006 and 2007 seasons the NFL redefined the pass defensed statistic. The number of passes defensed dropped significantly across the board. This change highlights an important concept regarding all three unofficial statistics. The NFL does care how solo tackles, assists and passes defensed are defined despite labeling them “unofficial.” Therefore, analyzing this data for subsequent changes will be an ongoing process from year to year.

Second, there are still some NFL stat crews that give the benefit of the doubt to the defender even post 2006. In the five-year (2008-2012) comparative study significance evidence of bias was found with the way six NFL stat crews award passes defensed. Stat crews that historically award higher number of passes defensed are Baltimore, Buffalo, Cincinnati, Detroit, New York (Jets), Philadelphia, San Francisco and Seattle.

One interesting result was that no stat crew awarded significantly less passes defensed only these six awarding more. Of course, this doesn't mean that some stat crews aren't less likely to score a play as a passed defensed, it just means that the study wasn't able to find enough evidence to support this hypothesis.

Finally, even though these six stat crews show significant evidence of awarding more passes defensed in a mathematical sense, the difference isn't large enough to be very significant in IDP fantasy football leagues.  There simply aren't enough passes defensed total for the stat crew's bias to make much of a difference. One of the most “generous” stat crews over the last five years including 2012 was the one in Baltimore.

As you can see by the very low p-value percentages there is significant evidence that the Baltimore stat crew is awarding a high number of passes defensed. However, will 10, 15 or even 20 extra PDs for an entire season when spread out to the entire defense create much of an advantage for IDP players in that stadium? I don't think that's enough of a difference to consider when looking at IDPs.

There is only one strategy that I would consider using based on these findings. If I had a tough start/sit decision that I couldn't make using other variables I would lean towards the defensive back playing in Baltimore, Buffalo, Cincinnati, Detroit, New York (Jets), Philadelphia, San Francisco or Seattle over a player in one of the other 26 NFL stadiums.

The results for solo tackles and assists were much more advantageous and I touched on a few strategies in parts one and two. But I think it's important to wrap up the series with a comprehensive strategy to take advantage of NFL stat crew bias. I call it studying the splits. In this case, focusing on differences between home and away for individual players and stadium venue in general for any player.

Splits have always been a big part of baseball analysis. There are home/away splits, day/night splits, weather splits, and many more. While this data is more predictive in baseball due to the increased sample size, it can still have value in fantasy football.

As I touched on in part two, there are potentially tremendous differences in how your IDP players score at home as compared to their scoring in various road venues. Knowing which stadiums are more likely to award solos vs assists vs shared solo/assist will lead to better start/sit decisions throughout the fantasy football season.

Too many times fantasy football owners only look at season totals when evaluating players. I urge you to make that one extra click and compare the game by game scoring of players you're considering drafting, trading or starting. Compare IDP's solos and assists at home vs the road.

It's also helpful to analyze game by game scoring to evaluate a player's consistency so you can make a note of that variable while you're there. Consistent scoring from your IDPs is essential for team success.

There are two ways I'll continue to help IDP owners exploit these stat crew differences. The first is to identify each crew's philosophy on scoring solos and assists to better prepare IDP owners for how players will be scored at each stadium. Reference and bookmark part two for full NFL stat crew data on solos vs assists from the last five years.

The second is to continue to monitor these splits in 2013 and beyond. I'll be looking for changes within each individual crew and for league wide definition changes like the one prior to 2007. I know the NFL would like to see more consistency from the stat crews. But for now study the trends and take advantage of some good ole home cookin’.

Nate Hodges is a staff writer for PFF Fantasy. His content can also be found over at TopTierFootball.com. You can follow him on Twitter – @NateNFL