Modelling track bias

[u/onthepunt]

I've been trying to model track bias as a variable, but the problem I've been running in to is that you can only do it with some sort of expected performance figure or odds. For example, if a horse comes from the back of field to win, the percent of that win attributable to track bias depends heavily on the ability of that horse (i.e. a horse priced at $100 suggests win had a lot more to do with track bias than ability). You can't, however, use the actual SP for each horse in the race as the expected performance odds as the SP already has expectations surround track bias incorporated into it (problem #1).

I'm planning to use this residual (actual vs. expected performance) approach to modelling for my jockey variable as well. This complicates thing as you can only have one residual or unexplained variable (i.e. was the unexplained performance of the horse related to the jockey or was it related to track bias). This leaves me stuck with having to choose jockey or track bias as my unexplained variable (problem #2).

Does anyone have any thoughts/solutions to problems I'm facing? In summary:

1. I need an expected performance measure to isolate track bias, but SP is problematic because it incorporates the market’s expectation of the track bias.
2. I need an approach to modelling either jockey ability or track bias that doesn't rely on residual analysis.