Statistical analysis and quantification
We view the Secondary Handicapping Factors as those factors which are beyond the horse's control.
If it can be quantified it's a secondary factor
In other words, any existing factor with the potential to impact the outcome of a race, if it can be quantified, and, if it is outside the horse's realm of control; then we classify that factor as a Secondary Handicapping Factor.
There can be any number (dozens or in a race like the Kentucky Derby even hundreds) of secondary factors to rate from race to race, which must be quantified and accounted for.
This is accomplished largely through applied statistical analysis techniques involving mathematical ratios.