It's said that those who cannot remember the past are condemned to repeat it.  Actually, Burke is usually misquoted as having said "those who ignore the past are doomed to repeat it", but I just need an excuse to show off some new charts that I've developed for the new season, so either the quote or the misquote will suffice.

THE FOUR RATING SYSTEMS - ROUND-BY-ROUND TEAM RANKINGS

You'll recall that we used four different team rating systems last season, the MARS Rating System, which I've developed, and three other popular Systems in the Colley, Massey and Offense-Defense Ratings Systems. Throughout the season I commented on the extent to which, at any point in time, these four Rating Systems agreed or disagreed about the ranking of particular teams. This first chart provides the ranking data for all Systems and all teams across season 2012.

(Please click on this and all charts in this blog for a larger version.)

The chart for each team shows how the four Ratings Systems ranked that team at the end of each round of the home-and-away season. Note that the label ODM_Reg is the Offense-Defense Ranking for the regular version of the ODM system - that is, the version that aggregates rather than averages the scores when one team plays another for the second time in the season. To minimise the extent to which the line for one System occludes the line for another I've "jittered" the ranking data by randomly adding plus or minus 0.05 to each ranking.

For a little over one half of the teams - the Lions, Blues, Dons, Suns, Giants, Roos, Dees, Power, Eagles and Dogs - the four Systems were in broad agreement for most the season.

For Adelaide, MARS was the holdout. Even by season's end it could only manage to bring itself to rate them 5th-best, an assessment that was probably vindicated in the finals. MARS also had a different view of the Pies, though this time its view was mostly shared by Colley, with each System consistently placing Collingwood in the top 3 teams. Massey and ODM ranked them more towards the bottom of the top 8.

Colley held a higher opinion of Fremantle's credentials for much of the season and ultimately ranked them 7th, an opinion that was almost but not quite shared by the other Systems come season's-end. Similarly, MARS was a Cats fan all season long and still had them ranked 2nd at the completion of the home-and-away season while the remaining Systems recognised some late-season improvement by Geelong but had them ranked only 5th or 6th.

By mid-season all the Systems bar Colley had decided that the Hawks were the number 1 team, an opinion that Colley did eventually reach but only at the end of round 18 just after the Hawks had demolished Essendon. Colley then recanted, dropping the Hawks down a couple of places for the next few weeks, only to capitulate after the last home-and-away game was complete and agree that, indeed, the Hawks were the superior team.

Richmond's performances induced mild disparities amongst the Systems with Massey and ODM generally holding more favourable opinions than MARS and Colley throughout the season. Colley, meantime, steadfastly refused to rank the Saints any higher than 10th except after the final round of the season when it elevated them into 9th, still some 2 to 4 places lower than the other Systems ranked them.

Massey and ODM recognised Sydney as the 2nd- or 3rd-best team from about the middle of the season, an assessment they maintained throughout the remainder of the season. MARS and Colley both started with lower opinions of the Swans as the second half of the season commenced, but came to much the same conclusion as Massey and ODM as the season progressed.

OFFENCE VERSUS DEFENCE - THE ODM VIEW

Overall, the ODM System appears to have adequately assessed the relative strengths of the 18 teams. Certainly by the end of the season it had come to rank the teams in much the same way as had the competition ladder, the rank correlation between its end-of-season rankings and actual ladder positions being +0.95.

One of the attractive features of this System is that it provides separate ratings for each team's offensive and defensive capabilities. In this next chart I've mapped these separate ratings for each team across the season.

The black line tracks each team's defensive ranking, the orange its offensive ranking, and the blue its overall ranking by the ODM System.

Focussing only on the rankings at the end of the home-and-away season we can see that the three rankings - offensive, defensive, and overall - are within a few ranking positions for many teams: the Lions, Dons, Cats, Suns, Giants, Hawks, Dees, Power, Tigers, Eagles and Dogs.

Amongst the seven remaining teams, three were significantly weaker defensively than offensively (Adelaide, the Roos and St Kilda) while four were relatively weaker offensively then defensively (Carlton, Collingwood, Fremantle and Sydney).

Overall, the rank correlation between the teams' final ladder positions and their defensive rankings according to ODM was +0.88, and between their ladder positions and offensive rankings according to ODM was +0.86. On this basis it'd be fair to conclude that offensive and defensive abilities were about equally important during the home-and-away portion of 2012.

MARS Ratings

MARS Ratings too did a reasonable job of reflecting relative team abilities. The rank correlation at the end of the home-and-away season between ladder position and ranking based on MARS Ratings was +0.96, the only significant differences being the rankings of the Cats (2nd on MARS and 6th on the ladder) and the Crows (5th on MARS and 2nd on the ladder).

I'll finish then with a chart of each team's MARS Rating across the home-and-away season.

Remember that, roughly speaking, each team will start the new season with a MARS Rating about half the distance between its end-of-season Rating and a Rating of 1000. (Note also that the Ratings shown here do not include the impact of the Finals series.)