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birth month and significance in racing, birth month of classic winners, breeding and statistics, horse racing and statistics, statistics
In an attempt to put some statistical shape to the chronology of good horses — how they perform by order of birth month — sales consignor Joe Appelbaum, analyst Rob Bingel, and number cruncher David Seguias worked up some data and commentary about the birth month of classic winners since 1970. Their work follows. Please feel free to comment.
By Joe Appelbaum, Rob Bingel, and David Seguias
Recently, our friend and fellow pedigree enthusiast David Seguias sent us a spreadsheet with the name and birth month of every American classic winner1 since 1970. A quick review revealed the need for context. How did the birth months of classic race winners compare with the general population?
Getting data from the Jockey Club is cost-prohibitive, but the Keeneland September yearling sale provides a big enough sample size (4,500+) to make the assumption that the sale serves as a proxy for the general Thoroughbred population.
Figure 1 shows the breakdown of the birth months for classic race winners since 1970 and compares them with the birth months of yearlings from the 2009 and 2010 Keeneland September yearling sales. The 2009 Keeneland birth months were slightly adjusted to capture the one-day leap-year effect of the foaling year of 2008.
| Figure 1. Success vs. Birthdate | |||||||
| Classic Race Winners Since 1970 | 2009 Keeneland September | 2010 Keeneland September | |||||
| January | 3 | 406 | 395 | ||||
| 1.8% | 7.8% | 8.1% | |||||
| February | 31 | 1,167 | 1,050 | ||||
| 18.3% | 22.5% | 21.6% | |||||
| March | 56 | 1,396 | 1,321 | ||||
| 33.1% | 26.9% | 27.2% | |||||
| April | 50 | 1,422 | 1,457 | ||||
| 29.6% | 27.4% | 30.0% | |||||
| May | 27 | 773 | 620 | ||||
| 16.0% | 14.9% | 12.8% | |||||
| June | 2 | 24 | 13 | ||||
| 1.2% | 0.5% | 0.3% | |||||
| July | 0 | 1 | 0 | ||||
| 0.0% | 0.0% | 0.0% | |||||
| Total | 169 | 5,189 | 4,856 | ||||
| 100.0% | 100.0% | 100.0% | |||||
Two months clearly stand out: January and March. While roughly 8% of yearlings in the 2009 and 2010 Keeneland September yearling sales had January birth months, only 1.8% of the classic race winners did. Conversely, 33.1% of the classic race winners had March for a birth month, which was higher than the 27% for both Keeneland September yearling sales. Meanwhile, for the remaining months, the percentages for the Keeneland September yearling sales and the classic race winners essentially mirrored each other.
What can we take away from this comparison?
The foremost observation is that the results are surprising! As readers of his book Outliers recognize, Malcolm Gladwell pointed out the inherent advantage that individuals born in early months within a given year group have2. In Gladwell’s book, hockey players with early birthdays benefit because they are more physically mature than their peers. By analogy, Thoroughbreds with January birthdays running in classic races against their younger peers should also theoretically own an advantage by being more physically mature.
Additionally, a number of economists have shown that yearling buyers prefer those foals born in January and February. Even without reading Gladwell, this is unsurprising – the aging of all horses to January 1 of their birth year would seem to make these “older” foals more desirable because they are larger, more mature and closer to training when they are viewed at the yearling sales.
However, according to Figure 1, this purchasing strategy puts a buyer at a disadvantage in the pursuit of Classic glory. Why is this? Are foals born in the more natural spring season stronger than their older peers? Are foals with lower expectations of success allowed to develop in a more healthy process that benefits their long-run performance?
There are a couple of points to remember when considering this data analysis.
First, the sample size for winners of classic races isn’t huge – only 169 data points. Still, there would have had to have been 13 classic race winners with a birthday in January to match the birth distribution shown in the Keeneland September yearling sales. In fact, there were only 3.
Second, this analysis looked at the birth months of classic race winners only and not all graded stakes winners. No assertions are made about the birthday distributions of graded stakes winners.
Third, the comparison of 40 years of results against the catalogs of the last two Keeneland Sales is hardly ideal. However, the results of these 40 years experience should be reflected in the current sales environment. If we accept the spring classics as the ultimate goal in American racing, then clearly these results have not been reflected by changes in breeding patterns.
In summary, a simple spreadsheet of data led to a perplexing question. Why do January foals fare relatively poorly in the classic races while March foals excel? This leads to a more economic question: Why are buyers ignoring this?
Rob Bingel Joe Appelbaum – Off The Hook
President, Equinistics LLC
bloodstock in the bluegrass 
Enquiring Minds Want To Know. Just goes to show there are always interesting questions and angles to be explorered.
“However, according to Figure 1, this purchasing strategy puts a buyer at a disadvantage in the pursuit of Classic glory. Why is this? Are foals born in the more natural spring season stronger than their older peers? Are foals with lower expectations of success allowed to develop in a more healthy process that benefits their long-run performance?” Also: “Why are buyers ignoring this.” INTERESTING. I look forward to hearing from others about this phenomena & their thoughts on WHY?
Something of a chronological bias here. You are looking at classic winners going back to 1970 and comparing them to yearlings of 2009 and 2010. The trend toward earlier birth months is relatively recent. Would have been better to compare the classic winners to Keeneland September yearlings of 1970, 1980, 1990, 2000, and 2010 instead. Or something like that to account for the differences in birth months over time.
When looking at some of the earlier crops, did you find particular trends in earlier or later birth months? Or is it something that changes from the effects of a group of relative outliers?
boojum, not sure how to get pre-internet data about the Keeneland Sale. The 2000 catalog isn’t online either, is it? Still, it would be interesting to look at the classic race birth month breakout by decade to see if there is a trend. I looked at this once and don’t recall seeing one, but I’ll put together the chart to verify. Sound okay?
boojum, out of 75 Classic Winners foaled in or after 1990, 3 (4%) were born in January. While the sample size is smaller, shouldn’t January foals outperform foals born in other months?