Here's how it breaks down: each team plays 16 games and collects anywhere from zero to 16 wins. That win total translates to a percentage of the possible wins, which we all recognize as "winning percentage." New England paced the field with 14 wins, followed closely by the Chiefs and a host of teams with 12 wins. Because this is the only set of outcomes that the teams are able to control themselves (ie, it's within their power to increase their win total if they play better), this percentage should be heavily weighted in the power ratings. After all, the idea is to win your games, right?

But 16 games isn't much of a sample, and you can't really say too much about the difference between the Patriot's 14-2, and say, the Eagles' 12-4. Is 125 percentage points a big gap? It's hard to rely on the significance of that difference by itself, but any discussion of power starts with your ability to win, so we assign a weight of 35.5% to the base win percentage.

We also need to go deeper and see how their opponents fared in their own games, to see whether one team played a relatively tougher slate of games against better opponents. For each team, we compile the win total of all 16 teams played during the season, to come up with an opponents' win total, out of a possible 256 (16 opponents times 16 games). The Chiefs' opponents won a total of 107 games between them, for an opponent win % of .418--not so good, and in fact the worst in the NFL. This is what I would call a bad sign. So long as I've been doing this, the RPI system has exposed a team that didn't actually belong. Last year, the lowest opponent win % was posted by the Packers, who promptly got shellacked by Michael Vick and the Falcons. By contrast this year, the Dolphins--a team with three fewer wins than Kansas City--faced opponents who posted 131 wins, or .512. A team with 10 wins is sitting at home, and you wonder if the Chiefs will perform as expected in the second round of the playoffs.

The opponents' win percentage can be skewed by the presence of very good or very bad teams within one's own division. Both the Titans and the Colts had percentages that suffered some from having Houston and Jacksonville in their division--although only to an extent, as the former two are in the overall top three. Similarly, Houston and Jacksonville gets boosts to their power ranking by benefiting from the high win totals of their divisional betters. Still, these numbers, while less volatile in their range than basic win totals, are subject to small sample sizes (only 256 games). So we assign a weight of 30% to this percentage.

Finally we go even deeper into the numbers, and record the winning percentage of the opponents of the opponents played in a season. This yields a sample of 4096 games for each team, which is plenty to minimize statistical error. These numbers are, like opponent win percentage, out of a team's control, but because there are so many games to review, noticeable differences between teams are more likely to be significant. Thus, we will weight these final figures 34.5%--not as high as the base win percentage, but more than opponent win pct.

To compute the power rating, first all the wins must be equalized. Because there are so many fewer games in a 16-game sample, than the 4096-game sample of OO Wins, a difference of just one win in a 16 game season can disproportionately skew the results. Therefore, each win must be multiplied by its proportion of all possible wins in the sample. For base wins, the number is .0625, or 1/16th. For opponent wins it's 1/256th (.00782), and for OO wins it's 1/4096 (about .002445). We then take these adjusted wins, wins of their opponents, and wins of _their_ opponents, weight them (multiplying them by .355, .3 or .345), and divide that number by the weighted result that would equal an average, .500 season. The same process is conducted as for the actual wins, and then that is divided by each team's result. The raw power number is then multiplied by 1000. What you end up with is the power rating you see in the table. The perfectly average score would be 1000, so the higher you are above 1000, the better. Conversely, teams under 1000 are less than average.

If we were to predict the NCAA-like "Final Four" from these rankings, we should expect to see a Patriots/Colts -- St. Louis/Philadelphia conference finals matchup. From here, those seem like the safest, most rational choices as well. The Titans could put a kink in those plans, but they have to head to New England after what will likely be a tough win against Baltimore if they win at all (although only the Ravens among playoff teams, did not finish among the top 12 in power ranking). The Colts should have no trouble with Denver, but Clinton Portis is a bit of a wild card. Kansas City, as noted, is a pick to exit in a surprise loss to the Colts, who seem to be peaking. In the NFC, the teams are much more scattered. Green Bay, Dallas and Seattle bring up what appears to be a lackluster slate of NFC teams--something fans have been mumbling about all year. It's a safe guess that any of the big four in the AFC (KC, NE, IND, TEN) will be favorably matched against whoever represents the NFC. St. Louis is home all the way through, which is huge for them, and unlike fellow paper tiger Kansas City, the Rams have an aggressive defense that will be helpful in the playoffs. Philly looks like the only truly legitimate team here, maybe Green Bay.

However, before we get carried away reading predictive tea leaves on who's in and out in the playoffs, a single game situation is entirely unpredictable. So what goeth before does not presage what cometh after. The power rankings do not take into account margin of victory, scoring differentials, injuries or the unusual motivations of homo sapiens. This rating concentrates on the sole outcome that matters...winning.

Enjoy reading over the results!

:: comments to mark bunster