My Power Ratings Explained
The Power Ratings are shown around a base of 100.0, which is considered to be an average team. A team with a Power Rating of 108 is eight points better than an average team; a team with a Power Rating of 91 is nine points worse than an average team. Although there is no theoretical limit to how high a Power Rating can go, in practice they almost never go below 80 or above 115.
How the ratings are derived:
The simplest explanation is that I look at the team's net points (points scored minus points allowed) and divide that by the number of games played, and add the result to 100. For example, after Week 4, the Patriots had outscored their opponents by 31 points, divided by 3 games is an average scoring margin of 10.3 points pluss 100 gives us an estimated rating of 110.3, and New England's rating is in fact 110.1. The longer explanation is that the scores of every game are adjusted based on the quality of opposition and whether the game is home or away. For the most part, these adjustments are minor, but in some cases they do reveal a team that is much better or worse than it appears at first glance. For example, Tampa Bay is still seen by the spreadsheet as an average team, despite the brutal 0-4 record.