The probability of winning compared to the odds is the formula for determining if a horse is a Jockey Jewels good bet. The best modern horse racing systems will indicate if a horse is a good bet and if it is truly meant to win. The clues to whether or not it is meant to win are contained in the pools. By comparing amounts in the pools and using betting patterns that the average horse player can't spot, many horse racing handicappers who use systems know when the insiders are betting on a horse.
Modern horse systems that teach the method of watching pools as well as the trainer moves and horse racing factors are the most likely to work.
But before you mortgage the farm and rush out to bet it all on a horse, a few words of caution are in order. There is no horse racing system on the planet that makes a profit all the time. At least, there is no known system that is being sold publicly. Who would sell such a system.