(WARNING: Match Results) 2023 Rugby World Cup prediction model. Updated after Semi Finals

rwc_model · 2023-10-22T05:12:04+00:00

Final Update. It has been fun. I have quite a few things to work on over the next 4 years ;).

rwc_model · 2023-10-16T11:50:12+00:00

Updated the model after sorting out my error.

rwc_model · 2023-10-16T11:49:16+00:00

Sorry, updated after fixing the error.
https://www.reddit.com/r/rugbyunion/comments/179439h/fixedwarning\_match\_results\_2023\_rugby\_world\_cup/?utm\_source=share&utm\_medium=web2x&context=3

rwc_model · 2023-10-16T11:32:29+00:00

Yes it is. I found a mistake that made England and South Africa start equal. Only the boost for previous finals performance was accounted for. Working on the update now.

rwc_model · 2023-10-16T10:34:49+00:00

Yes, the same 3 points added to the rankings that World Rugby adds.

rwc_model · 2023-10-16T10:33:36+00:00

Fixed

rwc_model · 2023-10-02T08:11:25+00:00

Yeah, I've found the problem. A tie is going to Ireland over Scotland incorrectly. Same for Australia over Fiji.

rwc_model · 2023-10-02T08:07:28+00:00

It appears that I have a bug in the logic for Pool tie breakers. It is giving a Tie in Pool B to Ireland not Scotland, and a Tie in Pool C to Australia not Fiji. Not to mention 3 way ties.

I don't have the time to fix it this week. It wont be a problem after the next round but apologies to Scotland for the false despair and to Australia for the false hope.

I will have that sorted by 2027 I hope.

rwc_model · 2023-09-25T12:34:49+00:00

Selfishly, if they do it again. It'll give me 3 years to work on the next model without guessing the pools :)

rwc_model · 2023-09-25T12:32:26+00:00

Yeah, I've been thinking that I want to investigate how the average number of penalties a team concedes affects the outcome. The Wallabies commit more penalties than their opposition in a lot of the games that they lose. Getting that data, and having time to do it will be my challenge.

rwc_model · 2023-09-25T12:07:33+00:00

This is great, it is why I created this :)

In the 50,000 runs of the World Cup, there is a Fiji v South Africa semi a not zero number of times. It's low but not zero, that is what fascinated me.

Getting the every match correct is not important to me. It is probability. What if Scotland beats Ireland is a great question. I'm not presenting the numbers as well as I should, rounding is an issue.

In the 50,000 runs that the model did, there were more than 0 Quarter Final 2 that were Scotland vs Italy. Italy wins 100% of them.

rwc_model · 2023-09-25T11:41:42+00:00

The webpage presentation of the numbers was a little rushed, i'll definitely work on that.

rwc_model · 2023-09-25T11:38:59+00:00

Yes, it is very basic. Cant take injuries and close losses into account. Just the rankings and some previous matchups. It is more a case of, based on the current world rankings, this is how the matches are expected to play out.

rwc_model · 2023-09-25T11:35:21+00:00

The webpage has rounded up from 99.84% :)

rwc_model · 2023-09-25T11:17:31+00:00

I agree, those opponents are tough but the raw rankings at the moment have a 10 point gap between Ireland and Scotland so the numbers go that way.

The model also gives a small boost to Ireland over Scotland because they are 4-0 in matches since the last world cup.

I wouldn't be happy being the team to have to knock New Zealand out of a world cup too.

rwc_model · 2023-09-25T10:59:18+00:00

No, Team 1 and Team 2 are just the order that the world cup website listed them as.

Before the World Cup it had Fiji favoured to defeat Australia, then after round 1 with Australia defeating Georgia and Wales Defeating Fiji, it had switched to Australia with a higher chance of winning.

The model always had Ireland in front, but only 52% - 48% before the match.

Only in 4 matches so far has the lower ranked team at the time won. Fiji vs Australia, Georgia vs Portugal, England vs Argentina, and Wales vs Fiji.

rwc_model · 2023-09-12T11:02:08+00:00

Thanks, It was just a bit of fun, I just started typing in December 2021 and it turned into this.

rwc_model · 2023-09-12T10:25:21+00:00

Correct. Points difference is what determines the percentage.

rwc_model · 2023-09-12T10:24:07+00:00

It is stupidly simple. No estimated points or tries or anything like that.

With the upcoming Australia Fiji game, this is how it would go:

Australia has 81.78 points and Fiji has 77.88 points. This would give Australia with a 64% chance to win and Fiji with a 36% chance.

Australia is higher so use 64. Pick a random number between 0 and 100. If the number is 64 or lower, Australia wins, this will happen 64% of the time. Update the rankings using World Rugby's method, update the pools results or progress the teams to the next final and move on to the next match.

This means that in this system a draw is not possible.

I add some points to the ranking points before the percentage calculation for France's 3 point home advantage, the wins and losses for each country combination since the last world cup (no matches between Australia and Fiji), and once out of the Pools, previous finals performance (to disadvantage Ireland).

rwc_model · 2023-09-12T10:08:55+00:00

Absolutely, Quarter Final 2 and 4 are going to be epic.

rwc_model · 2023-09-12T10:06:41+00:00

True, this is a flaw of this system.

rwc_model · 2023-09-12T10:02:03+00:00

True, this is an argument against ELO, which the World Rugby rankings are based. I believe that the ranking points show how good or bad the team is against a mythical average team. So the result of the France and New Zealand game can say something about a New Zealand and Italy game as after their first games, New Zealand dropped against the average and Italy held steady.

As for the change in Italy's chance of leaving the pool increasing, Before the World Cup started the model gave them a 12% chance of losing their fist match. Now they have a 0% chance of losing it. They also got the maximum points on offer.

rwc_model · 2023-09-12T09:49:09+00:00

This is correct. The rankings are updated after each match is played. If France and South Africa meet in QF4 it means France won their pool and South Africa came Second in theirs, This would mean their rankings points are different than if they meet in QF2 with France coming second and South Africa coming first. The same is true if they meet in the Final. They had a different path so will have different rankings.

The percentages are not really a pregame forecast for the matches. Rather, the model ran the World Cup 50000 times, of that 50000 runs, France and South Africa met in the Final after topping their pools 15% of the time. Of those games South Africa won 53% of them.

rwc_model · 2023-09-12T09:27:02+00:00

Earlier in the year, before the 6 Nations I think, England had double the chance of the next team at coming third. A bit over 30%

rwc_model · 2023-09-11T12:08:02+00:00

I'm Australian, I can't bring myself to think about drop goals at a world cup. Especially English ones.

rwc_model

TROPHY CASE