In 2yo Maiden stakes a horse which finished 2nd last time out is 3 times more likely to win than a horse which did not

Impact Values and Horse Racing

In 1974 an American called Fred Davis produced a book titled "Percentages and Probabilities". He displayed tables which included a new statistical technique for analysing horse racing information - the Impact Value.

Other work soon appeared such as the excellent book "Winning At The Races" by Bill Quirin. Nearly all US handicapping experts have mentioned impact values somewhere in their books.

The past ten years has seen impact values really take off in the US. Their importance is now worth more than speed figures in 'Handicapping' software packages.

Here in the UK impact values are mostly ignored. It seems we are too obsessed with form figures, top trainers and jockeys, 'hyped' horses, newspaper naps and tipsters. Only Nick Mordin promotes the use of impact values. You can read his excellent work in the Sporting Life / Racing Post Weekender, and in his own books.

What Exactly Is An Impact Value?

An impact value is a statistical technique which produces an index derived from the percentage of winners having a characteristic divided by the percentage of starters having the characteristic. Lets look at some examples.

last time out winners

Examining 69234 runners in 6678 races on the all weather we find that 5548 were last time out winners. Of those last time winners 1107 went on to win this race.

IV=% of winners that were LTO winners / % of runners that were LTO winners

IV=(1107 / 6678) / (5548 / 69234)

Impact Value=2.07

This means that, on the all weather, a last time out winner is twice as likely to win than a horse who did not win lto.

first run on all weather

22208 horses ran in 1896 3yo+ Handicaps. 2513 of those horses were having their first run on the all weather. 144 of these 'first timers' won the race.

IV=(144 / 1896) / (2513 / 22208)

Impact Value=0.67

In 3yo+ Handicaps a horse having his first run on the all weather is 0.67 times less likely to win than a horse who has run on the surface before.

2nd LTO in 2yo Maiden Stakes

33476 horses ran in 3127 2yo maiden stakes on the turf. 2264 of them were 2nd on their last race. Of this group 636 won the race.

IV=(636 / 3127) / (2264 / 33476)

Impact Value=3.01

In 2yo Maiden stakes a horse which finished 2nd last time out is 3 times more likely to win than a horse which did not.

An impact value of 1.00 means that horses have won no more or no less than their fair share of the races. Below 1.00 means they are performing below expectation, above 1.00 means they are performing above expectation.

How Can Impact Values Help in Finding Horse Racing Winners?

There are two ways to use impact values. You can either look for positive features to determine if a horse is worth backing, or negative features when trying to eliminate horses.

But you should not look at the impact value figure in isolation. You should examine both the impact value and the ROI% figure.

A strong positive value for both of them is what you need to find as this indicates a group of horses who are winning more races than they should, and are going of at prices higer than they should.

Looking again at the 2yo maidens who were 2nd last time, they may have an impact value of 3.00 but a level stake bet on all of them would have made a 10% loss.

In 4yo+ long distance (12f or more) Handicaps on the all weather, Colts have an impact value of 1.84 and have also returned a profit of 32%. These are the kind of positive stats you should be looking out for.

 More Info on Impact Values - Horse Racing Stats Guide

Related Articles and Resources

• Stats Guide
• Horse Racing Stats Discussions in the Message Board

Article created 01-Jun-2000. Stats may have changed since.