2011 Final MARS Ratings and End-of-Season Ratings History

It's fitting that Geelong, after defeating the Pies by 38 points on Saturday, should finish the season with the highest MARS Rating.

In doing so the Cats have ended the season with the 3rd-highest end-of-season ranking of any team since 1999, trailing only the Dons of 2000, who finished with a Rating of 1,071.3, and the Cats of 2008, who finished with a Rating of 1,064.2 (though not with the Flag).

Combined, the Cats and the Pies were the highest Rated Top 2 teams we've seen since Ratings commenced. Their average rating of 1,059.2 was almost 3 Ratings Points higher than the combined average of the Dons (1,071.3) and Carlton (1,041.3) of 2000. Ranked Ratings for every season appear in the table below.

From the middle section of this table you can see that, as well as producing the highest average Rating for the Top 2 teams, this season also produced the highest average Rating for the Top 4 and the Top 8 teams.

Whether these high Ratings were due to the superior quality in historical terms of the teams at the top of the ladder, or instead to the especially poor quality of teams nearer the foot of the ladder is a debatable point since, MARS Ratings being zero sum, a relatively strong Top 8 means a relatively weak bottom 8.

In the lower section of the table I've calculated the Rating differences between teams of various MARS Ranks and then put these Ratings differences into an historical context too. From this data you can see that the Ratings difference between the team ranked 4th and that ranked 12th was at an historical high this season, as was the difference between the team ranked 4th and the team ranked 8th. The gap between the team ranked 1st and that ranked 4th was less pronounced in historical terms, while that between the team ranked 1st and that ranked 9th was also relatively high.

What should probably be most concerning to the AFL is the trend in the Ratings gap between 4th and 12th - on this metric we've seen the 5 largest gaps since 1999 in the most recent 6 seasons, and the 3 largest gaps in the most recent 3 seasons. We've also seen 4 of the 6 largest gaps in the Ratings between teams ranked 1st and 9th across the past 5 seasons.

Narrowing our attention back to this year, it's interesting to note the level of momentum in team Ratings when you separately consider the movements in their Ratings during the 1st and 2nd halves of the season.

As the table at left shows, only 3 teams recorded movements in their MARS Ratings in different directions across the two halves of the season. Essendon gained 10.5 Ratings Points (RPs) across Rounds 1 to 12 only to drop 11.8 RPs across the remainder of the season, while St Kilda shed 5.7 RPs in the first half of the season and gained 14.8 RPs in the second half, and the Bulldogs shed 13.5 RPs during the first half and gained 3 RPs in the second half.

All 14 remaining teams either gained RPs in both halves of the season or shed RPs. 

Collingwood, despite being one of the teams to gain RPs in each half of the season, nonetheless had very different halves. They gained 30.4 RPs across Rounds 1 to 12, but only 1.1 RPs across the remainder of the season, dropping more than 12 RPs after Round 23 of the regular season.

Geelong, Hawthorn and the West Coast were perhaps the most consistent gainers, each acquiring between about 16-20 RPs in both halves of the season.

Putting these single-season Ratings changes back into an historical context (and here comparing one end-of-season rating with the next), we find that:

• Adelaide recorded its largest single season Rating decline this year (breaking the record it set only last season)
• Collingwood recorded its 6th consecutive season of Ratings increase
• Fremantle recorded its 2nd-largest single season Rating decline (after last year recording its 2nd-largest single season Rating increase)
• Hawthorn recorded its 2nd-largest single season Rating increase, which represented its 6th Rating increase in 7 seasons
• The Roos recorded their 2nd-largest single season Rating increase 
• Port Adelaide recorded its 2nd-largest single season Rating decline and its 6th decline in 7 seasons
• West Coast recorded its largest single season Ratings increase and the 2nd-largest increase of all teams since 1999

Though a number of the movements I've highlighted here might suggest that Ratings tend to trend from season to season, at least for these teams, perhaps the more general behaviour is for Ratings to exhibit regression to the mean. To investigate this phenomenon I produced the following table, which records the end-of-season Rating for each team, colour-coded to denote whether the Rating is higher (in green) or lower (in red) than the Rating for the same team for the previous season.

The four columns on the far right record the number of pairs of seasons for a particular team where its Ratings rose in both seasons (U+U), fell in both seasons (D+D), rose in one season and fell in the next (U+D), or fell in one season and rose in the next (D+U). Regression to the mean would suggest that the number of (D+U) and (U+D) season pairs should outnumber (D+D) and (U+U) seasons.

What we see instead is that: 

• teams that register Rating increases in one season are slightly more likely to register another increase in the following season. Of the 92 teams that registered Rating increases in one season, 50 (about 54%) registered a Rating increase in the subsequent season also. 
• teams that register Rating decreases in one season are also slightly more likely to register a Rating increase in the following season. Of the 84 teams that registered Rating decreases in one season, 44 (about 52%) registered a Rating increase in the subsequent season.

These trends are by no means consistent across teams. Carlton, Collingwood, Fremantle, Port Adelaide, St Kilda and Sydney are most notable for producing back-to-back Rating decreases or increases, each having done so in 7 (or in Collingwood's case 8) of the 11 pairs of season since 1999. Also, Hawthorn and Collingwood are remarkable in their ability to string back-to-back Rating increases together across seasons. Collingwood's done this 7 times and the Hawks 5 times.

Conversely, Essendon, the Roos and Melbourne are notable for their tendency to follow seasons of Rating increase with seasons of Rating decrease and vice versa. They've each done this for between 7 and 9 of the 11 season pairs since 1999.