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The NRL is reaching the business end of the competition, and fans are now facing the distinct possibility of some unfamiliar teams contesting for the trophy at the pointy end of 2015.
Since the competition expanded to an eight-team finals series, there have been some winners and grand finalists very much unfancied at this time of year. Most notably the Wests Tigers in 2005 and Parramatta Eels in 2009.
We can look at previous years to see how likely your team is to be there or even win on grand final day based on the season they had.
2015 NRL GRAND FINAL KICKOFF TIME
To do this I have used a stat called PyEx, which determines the possibility of each individual team winning the grand final since 1999 with seven rounds to go in the competition.
PyEx is calculated by dividing the square of the points scored by the sum of squares of the points scored and points conceded.
It works better than for and against because it corrects for high and low-scoring teams with the same for and against. A team that concedes less will win more often.
Its predictive capabilities, despite the uncertainties of predicting this far out and the fact that it depends on who you’ve played so far, aren’t too bad.
I have uploaded a histogram of PyEx values plotted against the probability of winning the grand final,
Probability of winning Grand Final vs PyEx pic.twitter.com/12vNENAj31
— Nathan Absalom (@Nathan_Absalom) July 21, 2015
or making the grand final
Probability of Making Grand Final vs PyEx pic.twitter.com/uv3ajkNPeg
— Nathan Absalom (@Nathan_Absalom) July 21, 2015
on Twitter.
As you can see, the better your PyEx, the farther you’ll go in the season. Teams that have a PyEx of 0.75 or higher winning the grand final 28 per cent of the time and making it 57 per cent of the time.
So, should you buy grand final tickets?
Buying tickets to the grand final can be a costly experience at this time of year if you only really care about your team. It can be much worse if you have to travel South from Queensland or even across the Tasman.
I had to fit a very rough model to the histogram (in red on the graphs on Twitter) to predict the chances of each team to make the grand final, or win it, this year.
It suggests that fans of the ladder-leading Brisbane Broncos should multiply the cost of their tickets by 2.7 to reflect their 37 per cent chance of making the grand final, and the North Queensland Cowboys by six 5 to reflect their 15 per cent chance. Disappointingly, the Sydney Roosters are a better than even chance of making the grand final.
Roosters and Broncos in the box seat
The Roosters are the team that is most likely to be victorious the grand final with a 28 per cent chance of winning. They are the highest ranked side on PyEx, which has actually won half of the grand finals in this time period.
The Roosters sit ahead of the Broncos (18 per cent) due to their impressive defence, but the Cowboys (8 per cent) are holding their lofty position on the ladder. Unfortunately, the 2014 premiers South Sydney Rabbitohs (7 per cent) have to really improve their form.
Outside of the current top four, the Melbourne Storm are the best chance (10 per cent), and as good as Billy Slater is, I would not be ruling them out this year either.
The Canterbury Bulldogs, St George-Illwarra Dragons (both 5 per cent) and the New Zealand Warriors and Canberra Raiders (both 4 per cent) have outside chances, while the Cronulla Sharks are less likely to win (3 per cent).
The one caveat is…
If you think this has been an even year, you’re right. The standard deviation (a measure of the spread of data) is very low this year, second only to 2006 since 1999.
Whilst teams in the bottom half of the eight have to improve to have a shot at the title, it is not an insurmountable task to match it with the teams right at the top. Whoever wins the grand final will be playing better footy in September and October than anyone has so far this year.
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