EDIT: see page 2 for this year's results!

The Breeders' Cup is always difficult, but this year we have an additional challenge: we don't know how Del Mar is going to play. Will it favor the home team? How can we predict whether performances across the country will translate to success in California?

Now we do have some precedence if we look at other BC's contested in California: 58% of dirt BC winners in California had a previous win at the host track, while 63% of them had a win in California. Meanwhile, only 27% had a previous win at Belmont, even though 45% had raced there at some point.

But this is a pretty reductive way of looking at things, right? A lot of people (rightly) point out that we don't know how many of these horses were favored and how many of them ran better (or worse) than expectations. So very long story short, I decided to address this issue by coming up with a formula that normalizes a horse's performance to their odds, for a value that I will refer to as a true differential. The formula is as follows:

True differential = (odds to $1) - (finish position/field size x 10)^2

With this formula, a score of around 0 means that a horse ran pretty much exactly as expected. A negative score indicates they ran a disappointing race, whereas a positive one means they exceeded expectations. This formula is rough and has two huge weaknesses: a horse at high enough odds will exceed expectations by running last (only one horse had this problem, Hot Number in 1993, and he was removed from the dataset), and it struggles badly with coupled entries (which are mercifully no longer a problem). But I think it passes the eye test, and I'd be interested in seeing if others agree.

For example, by this measure these are the most disappointing performance in California BC's since 1993 (unfortunately I don't have the charts for the 80's races): Jewel Princess, Cuvee, Touch Gold, Rich Tapestry, Princess of Sylmar, Daredevil, Close Hatches

These are the most expected performances: Flat Out, Tapiture, Beholder (2013), Iotapa, Shanghai Bobby

And these are the most unexpected: Arcangues, Ezzoud, Dawson's Legacy, Spelling Again, Take Charge Brandi, Pleasant Tango

This allowed me to generate graphs like this, to gauge the performances of horses who prepped at different tracks:

True differential values are on the left. Again, a 0 means a horse ran exactly according to their odds. If the middle line (the median) is higher, that indicates that those horses ran better than expected, whereas a lower line means they were disappointing. This graph therefore indicates that mares who prep for the Distaff at Santa Anita run significantly better, relative to their odds, than those who prep at Belmont (confirmed statistically but this post is verbose enough, happy to provide details if asked). Keeneland is included in these graphs because it is the third big prep location, but there weren't many interesting effects to report regarding it.

I generated these graphs for every BC dirt race, collected in an album here: https://imgur.com/a/yJWfp

In short, the Distaff shows the greatest effect. Belmont preppers as a whole run significantly worse than Santa Anita preppers in these races, and Santa Anita preppers on average run better than expected, but the effect is found only for two-turn races. In fact, horses who prep at Keeneland run slightly better in these one-turn races and there is no difference whatsoever between Belmont and Santa Anita preppers!

So this was really interesting, but something kept bothering me- just because a horse preps at Belmont doesn't mean that they actually like or run well at that track. So what happens when we look at prep performance in addition to location?

Incredibly, horses who win their prep at Belmont run worse than those who lose their prep at Belmont. This is a robust, reliable effect. Just look at this incredible graph:

The median odds of horses who win their prep at Belmont are 9/2 (actually lower odds than Santa Anita prep winners, who are 6-1). The median finish is 5th, and the media true differential is a dire -20.00. Meanwhile, prep losers (median odds 14-1) also run 5th on average, with a median differential of -11.28. This effect is not seen across tracks: Santa Anita and Keeneland winners run better or equally compared to losers. Once again, this effect is only seen around two turns. Around one turn, Belmont prep winners run a full ten points better than Belmont prep losers.

I think there are many possible explanations for this:

-horses who dislike Belmont are more likely to appreciate Santa Anita, and vice versa.

-the crowd is not good at evaluating the chances of horses who prep at Belmont

-Belmont preps have greater depth than other prep races, so horses who run 2nd or worse are more likely to outrun their odds the next time out.

-or perhaps Santa Anita preps tend to have greater depth, so horses who are good enough to win are stronger contenders in the BC.

-the strength of Belmont preps may be continuously overrated by bettors, or a lack of speed from the east coast horses may put them at a disadvantage (credit to Diver52 for these hypotheses).

While I lean toward option #1, I would very much like to hear what people think of this because I am a lifelong east coaster. I am admittedly a very strong critic of the idea that the BC should be permanently located in California, and I think this provides evidence that horses from certain tracks are potentially disadvantaged by running on the west coast- but this is by no means a certainty. The next step is of course to examine the performances of BC horses on turf and at Belmont. Meanwhile, I'd like to stimulate discussion with the following questions:

1. Do you actually believe these results, or do you have questions or criticisms about the methods? If you believe them, why do you think we see these differences between Santa Anita and Belmont?

2. Why do you think two turn races are (possibly) more prep-dependent than one turn races?

3. Do you think Del Mar will follow this trend? Does it affect your handicapping approach at all?

4. Which horses are you most confident will perform well at Del Mar? Least confident?

Thanks for reading!