To me, that's the hardest part about this game: by the time you have enough data to conclude that something is working, the game has changed. The trainer population changes (e.g., Diodoro and Gargan at NYRA), "training techniques" change, the tools that competing handicappers use change (e.g., Timeform US, clocker reports, Maggie Wolfendale), the mix of races changes (e.g., more turf sprints), etc.

When you are playing horizontally (I generally don't), where one or two hits or misses can make a dramatic difference in your ROI, it has to be even more difficult.