05/12/2009 12:32PM

Deceptive Margins?


Mine That Bird's 6 3/4-length Kentucky Derby victory May 2 was the largest in 63 years. But is there any correlation between the size of a Derby winner's margin and his likelihood of success in the Preakness?

Here are the last 40 Derby winners, ranked from largest to smallest margins by number of lengths, and how they fared in Baltimore:

The quick answer appears to be that there's no positive correlation at all:

--In the last 40 years, Derby winners are 16 for 37 in the Preakness (Grindstone, Spend a Buck and Gato del Sol did not run.) The Derby winners with the 20 largest margins are 7 for 18 in the Preakness.  Those with the 20 smallest margins are 9 for 19.

--Breaking it down further by quartiles, the top 10 margins are 3 for 9; the next 10 are 4 for 9; the next are 3 for 10; and the 10 smallest margins are 6 for 9.

--Horses who have won the Derby by three lengths or more since 1969 are 3 for 9 in the Preakness. Horses who have won the Derby by less than a length are 6 for 8.

It's not a huge sample, but it's enough to discourage anyone from equating a lengthy Derby win with a higher chance of success in the Preakness. The common-sense explanation for the lack of correlation is that big margins of victory may say as much about the quality and performances of the beaten horses as they do about the winner.

This can make one sound like a killjoy about runaway winners such as, say, Rachel Alexandra and her 20 1/4-length Kentucky Oaks victory. But it doesn't diminish her excellent performance to note that the six fillies behind her were as weak a supporting cast as has ever run in an Oaks, and that most of them failed to fire even their tepid best shots. One who did run her race was the runner-up, Stone Legacy. A typical Oaks runner-up runs a Beyer Speed Figure of around 90 to 95; Stone Legacy ran a 75, consistent with her five previous Beyers, all between 70 and 74.

Imagine for a moment that Justwhistledixie, who would have been the strong second choice in the race, had run instead of being scratched, and had finished second, beaten 5 or 6 lengths. Would people be quite as excited about Rachel Alexandra and her Preakness prospects?