We track every prediction we make and compare it against the actual match result. Here is our performance, updated nightly.
Every match prediction is based on the Elo rating system. Each team starts at 1500 Elo points. Ratings increase when teams win and decrease when they lose, with the magnitude determined by the relative strength of the opponent.
Win Probability = 1 / (1 + 10^((OpponentElo - TeamElo) / 400)). This is the standard Elo expected score formula used in chess and adapted for volleyball.
A prediction is correct if the team we said was more likely to win actually won. For a 60/40 prediction, we expect to be right about 60% of the time for those matches -- not 100%. The calibration chart shows whether our probabilities are well-calibrated.