As a horse ages we can expect some deterioration in performance but is age more taxing or as Dr Jones once said is it the mileage ?. We can take a look at this using MySportsAI, software that allows people with no Machine Learning grounding to create ML models to predict horse racing.
The first thing I am going to do with the software is slice the data down to only handicap races by clicking alongside raceType in the slice column and then clicking the slice data button at the top of the page.
Via the following screen we can now slice the data down to just handicaps for 2011 to 2015
I am now going to select age as a sole input feature to my model and click Run Model
This presents the following screen where I have selected 5 fold cross validation. This simply means that when I test my one feature model it will train the model on 4/5th of the model and then see how it performs on the remaining 5th. It will do this 5 times with different partitions or 4/5 to 1/5 splits.
Running the model gives me the following results, we will come back to these when I have carried out a similar run for number of previous races instead of age
I now return to the previous screen and select prevRaces instead of age
The results we get using prevRaces are as follows
We can see that prevRaces has thinned the horses out into rankings within each race better than age. this is to be expected as there are more individual values of prevRaces than age, age will only have values between 3 and 13 whereas prevRaces has values between 0 and 229. There are therefore more joint top rated horses with age as an input than there would be with prevRaces. We have to compare therefore roughly equal number of qualifiers, we cannot just say does the top ranked horse using age work better than prevRaces because there are far more top rated horse with age as the input.
Taking the top 3 rated for prevRaces would be roughly equivalent to the top rated for age. We can see that the return to win £1 on each horse would have yielded a loss of 2.41% for age whereas for the top 3 rated using prevRaces we have a loss of only 1.4%, better than backing all horses and losing 1.84%. The Brier skill score is also better for PrevRaces
My next step would be to take a look when we train 2011 to 2015 and then test for results on 2016/17. For the time being though Dr Jones would seem to have a valid point.