How Much Should You Forgive a Bad Run?

The rule of thumb for form reading

A horse that normally runs to 110 just ran to 102. Is it a 102 horse now? Still a 110 horse having a bad day? Something in between?

Most handicappers answer by feel. We measured it: how much of a horse's deviation from its own recent level shows up in the next start.

A bit under half

A horse carries a bit under half of any deviation into its next start. Run eight points below your level, and you are a few points worse next time — not eight. Run eight points above, and you keep a few of them.

The striking part is the symmetry. It is tempting to believe good runs are "real" and bad runs deserve forgiveness, and our own first measurement seemed to show exactly that: bad runs appearing to carry nothing forward at all. That result turned out to be an artefact of the extremes — a horse beaten twenty lengths was usually not ridden out, so its figure records a jockey's decision rather than the horse's ability, and those runs dominated the bad tail. Set those runs aside and the asymmetry vanishes almost everywhere. Forgiveness is symmetric. The only exception is Japan, where good runs carry more than bad ones do — noted, and treated cautiously until it replicates.

The share differs a little from country to country.

What changes the weight

That is an average. Three things move it a lot.

Ground. A run on heavy going tells you clearly less about the future than a run on a sound surface. This is the classic wet-track excuse, and it is the only excuse we tested that survives.

Surface. Dirt form transfers worse than turf form, in more than one country. Weight dirt lines accordingly.

Time. Form fades. A run from the last fortnight tells you far more than the same run four months old.

The runs to trust most

Three kinds of run that handicappers routinely discount turn out to deserve the opposite treatment.

A run at a materially different trip from the horse's recent races carries more forward, not less. So does a first run back from a break. So does a run into a hostile pace — the closer in a crawl, the front-runner in a duel. The mechanism is simple once said aloud: a run in unfamiliar conditions reveals something durable — a distance preference, a fitness level, a limit of the running style — and what it reveals repeats. A run in familiar conditions mostly confirms what you already knew.

The standard advice to throw out the wrong-trip run, the comeback run and the wrong-pace run is backwards. Those are the informative ones.

How to use it

Next time you look at a form line, resist both extremes. Nobody is as bad as their worst figure, and nobody keeps all of a career-best. Take the deviation, keep under half of it, discount wet and dirt and stale runs — and pay special attention to the runs that happened in the wrong conditions, because those are the ones that taught you something.

Every run on our racecards carries a rating on one comparable scale, which is what makes this arithmetic possible in the first place. The story behind the ratings is told here.