They have a rating for each race, think RPR or speed rating, or a personal rating sourced from God know's what, which for the sake of argument is out of 10. (If you like, you can say 10 is Grade 1 etc, downwards, but it doesn't really matter).
Here are the three sets of ratings:
Horse A: 5 7 9
Horse B: 8 8 7
Horse C: 7 6 10
Say they were each 2/1 to a 100% book? How would you want to bet ? What price would you want to take a value chance on each of them? Seriously.
Horse A: The improver. Looks like they're on for a Spinal Tap 11 out of 10.
Horse B: The consistent looking horse that sets the marker, lacking a 9 or a 10, but solid and genuine.
Horse C: The one with proven top class form, but just the once and last time out, possible regression to the mean material (aka bounce).
Maybe you'd take that last run away and look at them then - it would certainly change your perspective. Perhaps you'd want to take course, going, distance into consideration? Or their trainer or jockey? What if Horse A was a four year old filly trained by Stoute and ridden by Moore? What if horse B was trained by Peter Chapple-Hyam and he said she was as good as he's had? What if horse C was trained by Mark Johnston and the market was weak? Or any other extra bits of information. Some of which will be very important, most of which will be noise, and the difference between the two very hard to tell without the benefit of hindsight.
The beauty of gambling on horses in a nutshell. Well, actually no. These were the scores of the chefs competing just now in The Great British Menu ahead of their dessert course.
The result of course is irrelevant, but for completion here's how this particular race panned out.
Horse A: 5 7 9 6
Horse B: 8 8 7 10
Horse C: 7 6 10 8
(Which to be fair is how I would have bet, preferably at longer than 2/1)
And so the game would continue.
Numbers. Stats. Beautiful. Maths is poetry. Imposing order on chaos.
I've spent a lot of time with actuaries. They like raw data. They like reduction. They're very, very clever people and often complete idiots. Their downfall? People are irrational. As are horses. Be careful out there...