Using each horse's last five actual odds, we generate a predictive odds line to compare to actual odds. Then using a range, say +/- 25% we see who is falling inside or outside that range. Naturally there could be ways to make some adjustments based on finish last race or two, and class drops/rise, etc. I would make the average of the odds an exponential one, so that the last two carry more weight than previous three.
I know using a range, + or - 25%, is just a starting point. Using excel if you wanted, you could use a range within +/- 2 sigma limits or more. I know from following odds and betting for a long time, that often there will be only horse that will vary a lot from the ML. And often, there will be several.
The following chart(see link) shows three horses out of 8 that are outside those limits. Since the #1 is only slightly outside the 25% range, I'd only look at the #4, who is -61% below the predictive odds and #5 who is +45% above the predictive odds line. Is there some factor in their pp's that warrants #4 being bet much below where it usually is bet? Or does the #5 have the kind of value over its usual odds line? We've all seen a horse that's cold on the board, nothing's simple in this game.
https://docs.google.com/document/d/1...it?usp=sharing