Simulating the Finals for 2015 - Before Week 1

This year, I think the trickiest part about forecasting the Finals series is deciding how relevant recent Finals history will be in the current season. As we'll see from the results of the simulations, the TAB Bookmaker appears to have discounted history somewhat, though he also probably disagrees with some of the Team Ratings of the MARS System.

Over the 15 years from 2000 to 2014, teams that finished higher on the ladder have defeated teams that finished lower on the ladder:

  • In 41 of 56 Qualifying and Elimination Finals (73%)
  • In 26 of 30 Semi Finals (87%)
  • In 25 of 30 Preliminary Finals (83%)
  • In 7 of 15 (decided) Grand Finals (47%)

Combined, that means teams higher on the ladder have won 76% of the time.

So, when you build a statistical model based on this data, it places a heavy emphasis on the designated Home team in each game (ie the team from higher on the ladder). That's reflected in the large intercept term in the binary logit model I've built using the Finals data since 2000, which is:

ln(Prob(Home Wins)/(1-Prob(Home Wins)) = 9.77 + 0.02754 x Home Team MARS Rating - 0.03642 x Away Team MARS Rating

What's curious about this year is that the Minor Premiers, Fremantle have a MARS Rating that ranks them only fifth amongst their peers, which, when you use the model, despite its bias towards designated Home teams, a status that Fremantle will always enjoy, makes them slight underdogs against the Eagles, more substantial underdogs against the Hawks, only slight favourites against Richmond, and only comfortable favourites against the four other Finalists. These and all the other team-versus-team probabilities are shown in the matrix at right, which forms the sole input to the simulation process.

This input probability matrix implies the output probabilities shown in the table at left for each team's progression through the Finals series. It has West Coast and Hawthorn as both having about 60% chances of making the Grand Final, and West Coast as being slightly more likely of winning it. Fremantle, largely because of the modelled benefit of being Minor Premiers, but also because of the fact that they have the double-chance, are the third-most likely team to play in the Grand Final, and the third-most likely to win it.

West Coast, which at the time of writing is priced at $4.25 for the Flag on the TAB, is the only team representing value in that market. They also represent value at $2.15 in the market for just making the Grand Final, as do Fremantle at $2.50, but with a far less-attractive implied edge (only 3.5%).

Two teams represent value in the market for the losing Preliminary Finalists: Sydney at $2.05, and Richmond at $5.25.

Looking at Grand Final pairings, a West Coast v Hawthorn matchup is comfortably the most likely, it carrying a probability of about 36%. The two next-most likely matchups, each with about a 15% probability, are Fremantle v West Coast, and Fremantle v Hawthorn.

At current TAB prices that makes only the following pairings attractive:

  • Fremantle v West Coast at $7.50
  • Fremantle v Hawthorn at $6.50
  • West Coast v Hawthorn at $3.00
  • Hawthorn v Richmond at $51.00

As always, the extent to which you'll find these simulations appealling will depend heavily on how consistent your own assessments are with the probabilities shown in the team-versus-team matrix above.

On that front, I feel obliged to point out that, had you followed the wagering suggestions from previous simulations running up to the Finals this season, you'd have recorded a 17.89 unit loss on the 36 wagers recommended. It's really not been a great year for MoS wagering ...