Thursday, October 11, 2012

2012-10-11: NFL Power Rankings Week 6

It is now five weeks into the 2012 season and the season is starting to come into focus. The topic of many online discussions is this years performance of the NFC West division compared to last year. The NFC West is one of the best performing divisions so far this year, which is a far cry from last year. They are certainly doing well in our ranking system.

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 Falcons beat the Redskins 24 to 17, in the graph a directed edge from the Redskins to the Falcons with a weight of 7 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 is represented by the size of the node in the graph. The Pagerank algorithm used in this fashion has the nice effect of representing the strength of schedule. This should be of interest to many of the Houston Texan fans out there. The majority of the NFL Power Ranking sites out there, currently have Houston ranked number one. A simple glance at the schedule for the past five weeks would show that Houston has had a pretty easy season so far. They have played well so far and this week when they play Green Bay should be a good game.

The numerical rankings are as follows:

RankTeam
1Chicago
2Green Bay
3San Francisco
4Minnesota
5Indianapolis
6St Louis
7Arizona
8Seattle
9Philadelphia
10Houston
11Baltimore
12Atlanta
13Jacksonville
14Dallas
15Detroit
16Denver
17New England
18NY Giants
19Cincinatti
20San Diego
21Pittsburgh
22Miami
23Washington
24Buffalo
25NY Jets
26Carolina
27Tennesse
28New Orleans
29Oakland
30Tampa Bay
31Kansas City
32Cleveland

-- Greg Szalkowski

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