The Ratings Percentage Index (RPI) is a mathematical formula used in various sports to rank teams based on their performance in past games or races. In horse racing, the RPI is often referred to as the VDW method.

The RPI method in horse racing involves assigning a numerical rating to each horse based on its past performances, taking into account factors such as speed, class, form, and other variables. The rating is then used to calculate the horse’s “index”, which is a measure of its overall ability relative to the other horses in the race.

The index is calculated by dividing a horse’s rating by the average rating of all the horses in the race, and then multiplying the result by 100. This gives a percentage value that represents the horse’s chances of winning the race based on its past performances.

For example, if a horse has a rating of 80 and the average rating of all the horses in the race is 70, then the horse’s index would be (80/70) x 100 = 114. This means that the horse is 14% more likely to win the race than the average horse in the field.

The RPI method can be a useful tool for handicappers in predicting the outcome of a horse race, but like all handicapping methods, it should be used in conjunction with other forms of analysis and expertise.