2013 : MARS, Massey, Colley and ODM Ratings After Round 5

Over on the Statistical Analyses blog I've been dedicating significant blog-space - or whatever it is you want to call the online equivalent of column inches - to the MARS Ratings of teams throughout football history.

In those posts the Ratings stopped at the end of last season. Now it's time to bring them up to date.

Last year's Grand Finalists, Hawthorn and Sydney, currently hold the two highest MARS Ratings while the next six places are filled by four other Finalists from last season (Collingwood, West Coast, Geelong and Fremantle) and two of this year's big-improvers in Essendon and Carlton.

Carlton leapt four spots just last weekend on the back of a solid win over the Crows, the Blues' victory leap-frogging them over a logjam of similarly-rated teams, the Crows amongst them.

That pushed the Crows out of the top 8 on MARS Ratings and had them join the Roos as the only teams from last year's set of Finalists to have MARS Ratings outside the top 8.

Comparing teams' MARS Rating and competition ladder positions reveals large differences only for the Gold Coast (16th on MARS and 11th on the ladder), West Coast (8th on MARS and 15th on the ladder), and Port Adelaide (13th on MARS and 2nd on the ladder). On balance, I think I prefer MARS' assessment of the two Coasts, while I fancy Port's true ranking is somewhere around the middle of what MARS and the competition ladder currently think.

Even MARS recognises that Port are a team on the way up though. Port has acquired almost 15 Rating Points (RPs) since the start of the season, second only to the Dons, who've pouched almost 18 RPs.

The Hawks, despite dropping just over 1 RP this week in their game against the Roos, are another team that's been a substantial net-gainer over the course of the first 5 rounds. They've gathered almost 9 RPs since the season's first centre-bounce.

More modest net gains have been recorded by Geelong, Richmond, Sydney and Carlton, the latter two teams grabbing a significant proportion of that net gain only last week.

The Roos, Gold Coast and Fremantle round out the list of RP-acquiring teams so far this year.

MARS Ratings being a zero-sum game, for every RP recipient there must be an RP donor, and it's been Melbourne, GWS and Brisbane who have functioned as the competition's blood type O teams over these early parts.

Slightly less generous contributions have come from the Saints, Eagles, Dogs, Crows and Pies.

We know then where each team's Rating has ended up and we know how far their Rating has travelled to get there, but we don't yet know the arc that it followed.

That's the role of this next chart, which tracks the MARS Rating of each team as at the end of each round.

Every one of those worms tells its own story about the progress of the team to which it pertains. (The GWS worm looks as though it fancies the ground that Sydney's worm is traversing far more than it likes its own patch of dirt.)

You might recall from last season that I also track the Ratings produced by three other Ratings Systems: the ODM System (explained here), and the Colley and Massey Systems (both introduced here). The numbers that these Systems produce don't have the same intuitive interpretation as do MARS Ratings where we know that the mean Rating is 1,000 RP (and, by the way, also now know that the standard deviation is about 20 RPs), but they do produce a clear ranking of all the teams each week.

(Note that, in producing this chart, I've employed a technique known as "random jittering" in which a small, random amount is added to every value, which here are ranks. This serves to separate what might otherwise be mutually obscuring lines.)

Unlike last year, there are remarkably high levels of agreement across the Systems about the approximate rankings of most teams at this point in the season. It's really only Port Adelaide and, to a lesser extent, Sydney and West Coast about which the Systems show any significant levels of disagreement. For Port Adelaide, it's Colley that ranks them many places higher than the other Systems, albeit more in keeping with their ladder position, while for Sydney and West Coast it's MARS that thinks most highly of them.

One of the most useful and interesting features of the ODM System is that it provides separate Ratings, and hence rankings, for teams' Offensive and Defensive abilities. Currently, most teams are ranked similarly on each discipline by ODM, as shown in the following chart (focus on the black and orange lines).

The exceptions are Fremantle, which the ODM System rates as being let down by its offensive abilities, and Geelong, where, instead, defence is assessed as the problem. 

In support of this assessment, the latest Team Dashboard reveals that Fremantle have scored only 439 points in all their games this season, bettering the scoring output of only Brisbane, who are 12th on the competition ladder, and the teams occupying the last four ladder positions. It also shows that Geelong have conceded 486 points in their games, placing them 7th amongst the teams in the top 8 in the competition, and that the Conversion rate that Geelong have afforded their opponents is the worst in the league.