There was a lot of traffic coming into Offsetting last year whenever a game using the WASP was playing on Sky, so I thought I should link back to my original post explaining how it works. Also, let me reiterate a few points that I have made in comments elsewhere.
- WASP is a way of calculating who is winning, rather than a prediction of who will win. By example, imagine the All Blacks were trailing Ireland 10-9 at halftime in a rugby test. Ireland are clearly winning (they have more points), but the smart money would still be on the All Blacks to win the match based past performance of the two teams. Similarly with WASP, it calculates the expected score in the first innings, and the probability of winning in the second innings if the average batting team were playing the average bowling team on that pitch. A team may have got its nose in front based on this measure, but still be expected to lose based on an assessment of its overall ability compared to the opposition.
- The WASP prediction depends on an input of the par score for the conditions (pitch, ground size, etc.) in which the game is being played. If Sky use the same graphics as last year, you can infer what Sky has chosen as the par score when they put up the WASP worm showing how the WASP prediction has evolved through the innings. The assumed par score is the number that WASP started at when 0 balls had been bowled.
- In the second innings, Sky round off the probability of the batting team winning to an integer percentage, so values of 0 and 100 are possible even if the game hasn't actually been won yet. (Again, this is based on what happened last year; I assume it will be the same this year.)
- Things can be messed up a bit if a batsman retires hurt and may or may not return to the crease. This happened in this NZ v England match last year when Guptill retired hurt and then returned late in the innings to deliver a staggering performance for a #9 batsman!
There is a new feature this year, which is a graphic showing what would need to happen in the next two overs (five overs a 50-over game) to bring the match back into 50-50 balance--that is, to bring the predicted score to par in the first innings or the probability of winning to 50% in the second innings.