On 2 December 2018, Bordeaux hosted PSG on matchday 15 of the Ligue 1 season. It was PSG's first draw since the start of the season. Final score: 2–2. Did you see the match? Fans who followed it closely say that PSG should have won. That, after all, was also what the pre-match predictions suggested…
Before the match… ---------------
There are many ways to make predictions. From pure guesswork to machine learning, from casual punters to multinational sports-betting companies, from reading the sports pages to Big Data, everyone has their own method (see in particular the features "Mathematics and sport", Tangente 168, 2016, and "The mathematics of betting", Tangente 175, 2017). Between these extremes lies a relatively simple method: the Elo rating system.

A team's probabilities of winning, losing and drawing as a function of the difference between the teams' Elo ratings (C = 100).