Overweight Horses Win Fewer Races

December 28, 2013 Posted in Racing by No Comments

slow horsePhoto by Magic Madzik

Horses that are asked to carry more weight than expected win fewer races than they should. Derek Simon over at the TwinSpires.com blog studied nearly 900 horse races to see if there was a statistically significant difference in win rates between “overweights” and horses that checked in on weight.

Note: The word “overweights” refers not to the weight of the horse itself, but horses that are asked to carry more than their assigned weight. This can be due to the jockey not hitting his target weight, for example.

It may not sound like shocking news that overweight horses win fewer races, but the author of the blog post did a well-planned statistical analysis to see if a couple of pounds really does make a difference in horse racing results. Instead of going with his gut feeling, he studied the results of hundreds of past races to see if a few pounds truly does make a statistically significant difference.

The author used two different statistical methods to see if overweight horses won fewer races than they should have otherwise. First, he used Dr. William Quirin’s impact value to divide the percentage of winners with a given characteristic by the percentage of starters with that characteristic.

With that number, Derek Simon was able to see if horses that weighed in overweight showed up in top spots less often than horses that came in on weight. This number serves as a good starting point, but it doesn’t necessarily tell you how much effect that one characteristic had on those outcomes. For example, Derek explained that horses with the letter “A” in their name also show up more often in winning positions.

So to further narrow down the numbers, Derek used an “odds-based impact value” calculation to base results not on the total field of horses in each race, but on the average odds of each horse in the race. I know this is kind of a poor explanation, but you can visit the blog post to see all the details here.

Anyways, the point is the author used two different methods to find out how much impact horse carry weights truly have on results. And in the end, he found that it does make a difference. Unexpected additional weight does cause problems for horses that want to win races.

Keep this in mind the next time you’re about to bet on horses.