Originally Posted by Raystef5845

I promised to give you the predictions for the group phase of the Rugby World Cup, as soon as we had the pre-WC ratings from World Rugby. The final ratings are in, so I attached the game-by-game probabilities, using World Rugby’s system, and then the fair decimal odds which are equal to 1/probabilities. According to the World Rugby system, they add three rating points to the home team rating and then find the rating difference of each team’s rating minus the opponent’s rating. The probability that the team will win is:

.5 + (rating difference)/20

There is a problem though. World Rugby has to cap the rating difference at +10 (or -10) to keep the probability between 1 and zero. I decided to make the limit 0.99 and 0.01, because having World Rugby predicting a probability of 1 just makes me crazy, and we don’t want that.

There are Groups A, B, C and D, each with 5 teams playing four games in a round-robin, so each group plays 10 games. Of the 40 games, 24 are maxed out with winning probabilities of 0.99 and 0.01. The other 16 games are much more competitive. I noticed that 7 of 10 Group A games are maxed out, compared to 8 of 10 in Group B, 3 of 10 in Group C and 6 of 10 in Group D. Group C should be the most competitive. There aren’t going to be many games worth betting on, but those will be hugely important, and keep the pubs busy. When we reach the quarter-finals, the rest of the games ought to be close, but World Rugby will not update ratings until after the WC, so we have to use pre-WC ratings. Of course, you could make big money on some big upsets and buy the first round.

Cheers
,
Ray Stefani