I am writing previews for the last 3 quarter finals. First up, Spain vs. Belgium then the next two will follow very soon! I will review the betting odds implied levels of the teams and as well as World Cup performances so far. I want to compare what I think the betting line should be to its current number.
Figure 1
The MIRs (market-inferred team rating) contain various adjustments. For example, for Spain’s RD3 game against Uruguay, Spain were not strongly motivated as they had already won the group. This will result in the MIR pushing down Spain’s overall rating when it is not deserved. This can be corrected by adding some small amount. Also, I improved the schedule adjustment for each team by varying the MIR rating of their opponents for each game. For example, Portugal’s lacklustre performances reduced their rating as the tournament went on so Spain are considered to play an opponent with a rating of +0.94 instead of, for example, a rating of +1.16 had they played Portugal in their opening match.
These adjustments help us make a more direct comparison of how the global sports markets rate each team. These MIRs will be very accurate as it’s only professional syndicates placing very large bets that significantly move the markets. We can see Spain are rated consistently highly across the tournament. It appears there may be a small drop off since the first two games but as they were so strongly favoured in those games (against Cape Verde and Saudi Arabia) it stresses various parts of the process (e.g., are they more favoured against these teams because there’s less likely to be a game state effect where they hold on for a narrow victory). Similarly for their round 3 game against Uruguay, it’s hard to quantify the impact of reduced motivation.
Spain’s MIR for the 2 knockout ties so far is +1.58. This means they would be expected to win by an average of 1.58 goals against an average world cup team (24th best team of 48). Spain’s performances have been consistently solid, between 1.5-2.0 goals better than their opponents each time (except for Uruguay, which has been rated upwards but even so, I think I should discount that match). Spain have not spent a minute losing so far and plenty winning which results in a game state adjustment of around +0.27. I am using a simple game state adjustment where I expect leading teams to underperform by about 0.55 goals per game. I am intentionally using one decimal place for performances and 2 for MIRs as I think it represents how much information each rating system contains (over these sample sizes).
Spain’s strong performances push their overall rating into the 1.67-1.83 region.
Belgium have had a bumpier ride. They were very ordinary against Egypt initially but bounced back with stronger performances against Iran and New Zealand. This pumped up their rating, and they went off even-money shots to win in normal time against a strong Senegal side. A poor performance (and an unlikely win) followed, resulted in a much lower MIR against the USA. The performance against the USA was a return to perform suggesting Belgium’s MIR will rise once more.
I don’t think there are any significant injuries or suspensions. This is entirely relatve – we’ve trained our ratings purely on the World Cup so far so it’s only of interest if a player who has been missing is now returning or vice versa. Amadou Onana picked up an unfortunate potentially long-term injury against the USA but had not featured heavily this World Cup regardless. Lamine Yamal missed minutes in Spain’s group games but similarly Doku (a player I rate highly) and De Bruyne have both missed games and could be used as fresh options for this game. I don’t think the potential lineups are a mitigating factor.
My ratings here show Spain as favoured by between 0.63 – 0.67 goals. Currently at 11am BST on Friday the market shows Spain as 0.85 – 0.95 goal favourites. I’m not sure how to explain the difference so I am siding with Belgium here.
Edit: I think there’s a problem with my approach properly respecting differing goal lines and total goals per game. Spain are posting these numbers on a lower total goal count than Belgium. I’ll work on that
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