Friday, December 21, 2012

2012-12-20: NFL Power Rankings Week 16

The NFL Playoffs are only a few weeks away. With the end of the regular season in sight there are a few trends that subtlety change the game. One of the trends is the weather. Tennessee is playing at Green Bay and snow is in the forecast. Another end of the season trend is displayed by teams that have clinched playoff positions. They rest their starting lineup and play backup players. That is more of a week 17 phenomenon but with Atlanta and Houston both at 12-2 for the season they may play some non-starters during the game. This ranking system is based on team performance and does not take trends like the weather into account.

Our ranking system is based on Google's PageRank algorithm.It is explained in some detail in past posts. A directed graph is created to represent the current years season. Each team is represented by a node in the graph. For every game played a directed edge is created from the loser pointing to the winner and it is weighted by the Margin of Victory.  

In the Pagerank model each link from a webpage i to webpage j causes webpage i to give some of its own Pagerank to webpage j.  This is often characterized as webpage i voting for webpage j. In our system the losing team essentially votes for the winning team with a number of votes equal to the margin of victory. Last week the Redskins beat the Browns 38 to 21, in the graph a directed edge from the Browns to the Redskins with a weight of 17 was created.

The season graph so far can be visualized in the following graph.

The Pagerank algorithm is run and all of the votes from losing teams are calculated. The nodes in the graph are given a final ranking and that ranking is represented by the size of the node in the graph. This algorithm does a much better job of taking the strength of schedule into account than many of the other ranking systems that are essentially based on win loss ratios. Atlanta has had a good season so far but their strength of schedule was the easiest of the entire league. Strength of schedule was based on performance from the 2011 season. Up until last week Atlanta was not considered a strong contender for the Superbowl but after shutting out the Giants, their performance shows the team is capable of a dominant effort against a quality opponent. Although with the Giants you have to wonder which team will show up each week.

The numerical rankings are as follows:

1NY Giants
2San Francisco
4New England
8New Orleans 
11Green Bay
16St Louis
18Tampa Bay 
23San Diego
24NY Jets
27Kansas City

-- Greg Szalkowski

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