If you are trying to handicap horse races, whether the thoroughbreds (flats) or handicapping harness races (trots) you know that class is a major factor in picking winners. The problem is that class is so hard to determine. At first glance, it is easy to say that a horse raced against tougher horses so if it drops today it should win, but we all know that just isn't the case. Class and form are closely related, in fact, in my opinion, class is form and form is class. Let me explain.
You may have a horse who won a Grade l race last year and who is now competing in a handicap race. It may be competing against horses who recently raced in claiming races. Does that mean the Grade l winner has a big advantage and should be the favorite? Not necessarily. It means you should give it some respect and check its workouts and whether or not the trainer can bring a horse back in condition to win, but the horse may be out of shape or at least not in good enough form to win.
When I try to determine the class of a horse, I look at the recent races to see what level of horses it competed against and then I look at its pace and speed figures. I want to see where it finished and how competitive it was at that level. That is the key to class and the one true way to compare horses. How well did the horse compete at the level it ran at. You can't just look at the purse of the race, but also how the horse competed.
By competed, I mean, did it contest the pace, and if so, how contentious was the pace? Did it finish well or win? If so, once again, how hard and how fast did it run? The only way to be able to handicap horse races, no matter what system you may use, is to develop skill and judgment so you can look at a horse dropping out of a race with stiffer competition and compare it to one who just won at a lower level and know which one is really the class of the race. That takes practice and if you're smart, good notes.