Summary
Off to a good start! The model predicted 6 out of 8 matches for a 75% accuracy in the first round.
The two games the model mis-predicted were Manly vs Bulldogs and Roosters vs Rabbits
Assuming a $1,000 initial bank, if we used a Kelly staking strategy to bet this round, we would have made a profit of $470. Despite high prediction accuracy, the accuracy of this staking strategy would have been 50% due to its recommendation to stake on two of the matches the model actually mis-predicted.
Using Kelly staking we would have bet big on the Tigers, and this is where most of the profit comes from; however if the Tigers had of lost, we would have actually lost $483 for the round, and our final bank would have been $517!
If we had of used the (more conservative) proposed staking strategy we would be up a modest $39. Using this staking strategy we would have staked on two matches and made profit on both (100% staking accuracy).
Detailed round overview
The model predicted 6 of 8 games (75% accuracy). The models accuracy was well above the average of the 2009-2015 historic round 1 results (53%) and was well above the 2015 results (25%).
The biggest upset to the bookmakers odds was West Tigers who beat New Zealand. The bookmakers had West Tigers at 2.65 to win (indicating only a 38% chance of win).
The model was successfully in predicting two of the three upsets to the bookmakers odds (West Tigers and Gold Coast to win).
The two games the model mis-predicted were Manly v Bulldogs and Roosters v Rabbits which were upsets to the bookmakers odds as well.
Despite our high predictive accuracy for the round, If we used the Kelly strategy to stake we would have staked on four games and lost on two of the matches (50% staking accuracy). But due to the win on the Tigers we would have still made a profit.
If we had used the proposed staking strategy, we would have staked on two games and won on two games (100% staking accuracy), but due to the conservative nature of the staking strategy would have only had a modest return of $39 for the round.
Detailed simulated staking
In accordance to our staking strategy we aren’t staking on anything until round 5, but lets take a look at what would have happened if we did bet. lets assume we started with $1,000 which is the actual current bankroll in my account.
(Full) Kelly staking:
The first game we would have backed (first game which had a positive Kelly fraction) would have been Manly v Bulldogs at odds of 1.70 to win. Our Kelly fraction was 0.07 which means we would have bet 0.07*1000 ($70 dollars). Bulldogs got up in an upset win (28 to 6 – yikes!). This would have reduced our bank to $930.
The next game we would have back would have been West tigers vs New Zealand, which was against the bookies tip by a very long shot (bookies had tigers at 2.65 indicating they though they only had a 38% chance of winning). My model had them at a 60% chance of winning so the discrepancy was BIG. The Kelly fraction was 0.41 which indicates we should bet 41% of our bank on this game… hmm seems very risky, oh well I have the excuse that the algorithm made me do it! The stake would have been 0.41*930 (our new bank after the Manly loss) which is $381.
Amazingly tigers did actually get up with a 34 to 26 win. We would have won big on this game, with a profit of (2.65*$381)-$381 = $629. Adding this to our bank we would have a new bank of $1,559
The next game we would have staked on would have been Roosters v Rabbits at 2.10 to win. Roosters got smashed 42 to 10 (great work algorithm lol). Kelly stake on this was pretty high at 0.18, so we would have lost 0.18*1,559 = $281.
And our bank would have went back down to $1,278
Our last bet would have been on the Gold coast to win against Newcastle at odds of 2.0 to win. Kelly fraction for this match was 0.15 so we wold have staked 0.15*$1,278= $192. Gold coast did indeed get up (30-12) and so we would have got a reasonable return of $192 ((2.30*$192)-$192)
This would have taken our final bank to $1,470 which is a profit of $470 over our initial bank.
Proposed staking strategy:
If we were using the proposed staking strategy which is to use a fixed (5% of current bank) wager on games which have a perceived probability > than the average of the perceived probability of historic false positives, then we would have only staked on two games:
Cowboys to win against the Sharks and Storm to win against the Dragons.
We would have first staked $50 on Cowboys at 1.35 which would have given us a profit of $20 taking our bank to $1,020. We would have next staked 5% of 1,020 ($51) on Strom at 1.38. This would have given us a $19 profit taking our final bank for the round to $1,039
Obviously this is a less risk adverse strategy and in this round would have yielded a lower profit than the Kelly strategy. However keep in mind that if Tigers had of actually lost, the final bank for the round would have been $517. Such is the rollercoaster ride of the Kelly staking strategy.
Table Summary of predictions vs actual results
| Tip | Score | Score Against | Result | True Positive | False Positive |
|---|---|---|---|---|---|
| Brisbane Broncos to win against Parramatta Eels while Away | 17 | 4 | correct prediction | 1 | 0 |
| Manly Sea Eagles to win against Canterbury Bulldogs while Home | 6 | 28 | incorrect prediction | 0 | 1 |
| Canberra Raiders to win against Penrith Panthers while Home | 30 | 22 | correct prediction | 1 | 0 |
| Wests Tigers to win against New Zealand Warriors while Home | 34 | 26 | correct prediction | 1 | 0 |
| North Queensland Cowboys to win against Cronulla Sharks while Home | 20 | 14 | correct prediction | 1 | 0 |
| Sydney Roosters to win against South Sydney Rabbitohs while Home | 10 | 42 | incorrect prediction | 0 | 1 |
| Gold Coast Titans to win against Newcastle Knights while Home | 30 | 12 | correct prediction | 1 | 0 |
| Melbourne Storm to win against St George Illawarra Dragons while Home | 18 | 16 | correct prediction | 1 | 0 |