MAFL 2012 : Team Dashboard for Round 22

The Team Dashboard for Round 22 is below, but before we get there, recognising that percentages might play a role in determining teams' final ladder positions this season, I wanted to share a simple way to estimate the effects of a single game result on a team's for-and-against percentage.

I covered this in detail a couple of years ago, but the simple heuristic that emerged was that a team's updated percentage could be calculated using this formula:

New Percentage = Old Percentage x (1 + (Points Scored In Game as % of Points Scored All Season - Points Conceded In Game as % of Points Conceded All Season))

To use this heuristic all we need to do is to assume how many points the team will score expressed as a percentage of the points it's scored so far this season, and how many points it will concede expressed as a percentage of the points it's conceded so far this season. We then subtract one from the other and this closely approximates the proportionate change in the team's for-and-against percentage.

Here's a worked example investigating the likelihood that Geelong overtakes West Coast on for-and-against percentage should the Cats win and the Eagles lose.

First, consider the Eagles. They've scored 2,174 points this season, so every 22 points they score roughly equates to 1% of their season total. Similarly, they've conceded 1,712 points, so every 17 points they concede equates to about 1% of their season total. If they lost then by say 66-136, then they would have scored about 3% (as 3 x 22 = 66) of their season total points scored, and would have conceded about 8% (as 8 x 17 = 136) of their season total points conceded and, as such, we'd estimate that their for-and-against percentage would drop by about 5% (ie 3% less 8%).

Now, their current for-and-against percentage is 126.99, so a 1% decline is about 1.25 points and a 5% decline is therefore about 6.25 points. Using our heuristic then we'd expect that their for-and-against percentage would drop to about 126.99 - 6.25 = 120.75 (say). The actual result for a 66-136 loss is that the Eagles' for-and-against percentage becomes 121.2, so the heuristic is reasonably accurate here.

Now let's assume that Geelong wins 126-54. The 126 represents about 6% of Geelong's points scored so far this season, and the 54 represents about 3% of the points conceded so far this season, so such a scoreline would be expected to lift Geelong's for-and-against percentage by about 3%, which is about 3.5 points, since their current for-and-against percentage is 115.98. Out heuristic then tells us that the Cats' for-and-against percentage moves to 115.98 + 3.5 or about 119.5. The actual result for a 126-54 win is 119.3, so the heuristic is, again, quite accurate.

So, even with the relatively unlikely outcomes of the Eagles going down to the Crows by 70 points and the Cats beating the Swans by 72 points, the Cats still don't do enough to overhaul the Eagles' current for-and-against advantage. To finish fourth, the Cats would need not only to close this gap but would also need the Dons to defeat the Pies. Little chance of a fourth-place finish for the Cats then.

Here's the Team Dashboard: