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The effect of draw bias on horse racing betting

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The draw for Flat season horse racing is often overlooked by bettors, but it can have an impact on the result at specific race courses. This article looks at the effect of draw bias in horse racing betting, and factors you should consider.

What is the draw in horse racing

Unlike the National Hunt season, nearly all flat racing events use starting stalls. The draw simply refers to the stall a horse will start the race from. The draw is normally chosen at random on the day the horses are declared to run.

Usually, draw 1 is on the left, while the highest number is furthest to the right - on left-handed courses the lowest draw is next to the inside rail, while the highest draw is next to the inside rail for a right-handed track. However, you should always research the course for changes.

Draw bias and the inside rail in horse racing

Draw bias refers to whether or not a horse has an advantage or disadvantage following the stall they have been drawn in. But why is this?

Imagine a 400m race in athletics, who would have the advantage if all lanes were not staggered? The inside lane would obviously hold an edge over the field as they have a shorter distance to the bend, in comparison to the other lanes.

Let’s use a hypothetical horse race to highlight how the draw bias can affect a horse based purely on the stall number they are drawn in.

Assuming the course is a left-handed circle, and the jockey and horse combined are approximately 4 feet wide, we can use a mathematical constant called Pi to calculate the additional distance for those horses drawn higher than lane 1 will need to cover.

If the radius of the circle is r, then the total length of one lap is 2πr. For the horse in lane 2, the radius becomes (r+4), so it has to cover 2π(r+4) in one lap, which is 2π(r+4) - 2πr = 4π ≈ 12.6 feet more. The image below simplifies this calculation

Computing the additional distance to estimate the draw bias for each stall.

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The table below shows the additional distance a horse will need to run if they stay in the same lane for the entire race:

Stall Equation Additional distance (feet)
1    
2  4π 12.6
3  8π 25.1 
4  12π 37.7

This highlights the advantage of being drawn in stall 1 - it clearly shows the further from the inside rail a horse is drawn the more unfavourable the effect of the draw bias can be.

If the horse drawn in lane 2 ran the entire race next to the horse in lane 1 it would have to run 12.6 feet extra in distance.

It’s very unlikely that a horse would hold their stall position for the entire race - as it’s such a disadvantage - but this diagram also highlights the difficulty in overtaking a horse positioned on the inside lane while negotiating a turn - needing to catch the horse and then conquer the additional distance of not being on the rail.

Generally, the inside lane is the most sought after, so why doesn't’ the horse on the inside always win?

Of course, horse racing tracks are not a perfect circle, and there are many other factors which can affect the outcome of the race, and also where the draw bias is.

Other factors affecting draw bias in horse racing

Draw biases can be affected by a number of other racing factors other than the inside rail, and given they are constantly changing it creates the perfect trading opportunities for the more informed bettor.

It would be naive to assume a draw bias based on rigid data, instead, your horse racing betting model should be fluid and look at a number of these other factors both when researching a draw bias and predicting one before the race.

You should consider the following factors when assessing the effects of the draw on the final result:

The shape and design of the course

British and Irish racing have a variety of courses which differentiate in both shape and length. Some tracks are designed with long sweeping bends, while others have no turns at all.

The position of the turns can also affect the outcome. For example, if the first turn in a race is shortly after the start, the outside runners will struggle to take the inside rail before the turn begins. Given it’s easier to overtake on the straight, if the run to the first turn is long, it gives the outside horses more of a chance to win the battle for the inside rail.

Races starting from a chute like in America can also create a bias. The length and angle it joins the first turn will affect the race; for instance, a chute connecting with a shallow angle to the first turn will often favour the outside horses, while an approach with a sharp angle will likely favour the inside runners.

The variation in course design is a prime example of why the severity of the draw bias is different from track to track.

Race distance

Races vary in length, understanding the effect of a draw bias over the distance is paramount to finding trading opportunities.

It is widely accepted that the draw affects shorter races - 5, 6 and 7 furlongs - more than longer races. If a horse on the outside misses the chance to gain the inside rail or doesn’t react to the break, it has less time to rally. Making this ground up on the outside can drain energy - as they have to run further -  and leave the horse short of the speed and stamina needed to recover.

Size of the field

The number of runners can also impact how the draw will materialise in a race; Smaller fields and the horses will all filter down to the inside rail, while for large races, the horses are likely to be spread across the track, as they will struggle to move from one side of the track to the other.  

This can also created a bias where certain good horses are bunched together in the draw while another is on his own. This can have an affect as the horse away from the strongest competitors will be blind to the other strong competitors speed and at a disadvantage.

The ground

The ground the race will be run on can also create a draw bias. There are numerous reasons why this may be the case.

For example, If it has been raining, the running could be affected by the course drainage; one section may be quicker than the rest - thus creating a bias.

What if the inside rail is the lowest part of the track, and is wetter compared to the other parts of the course? Therefore understanding how the horses perform in conditions, and knowledge of the course itself should be considered before declaring a draw bias.

The horse

Understanding the characteristics of the horses in a field is still fundamental when assessing a draw bias, and can also explain why certain horses perform well at a particular course and not on another, even when they may first appear to have conditions that suit.

If a horse likes to lead a race and is drawn in a good stall this would appear to suit him, while a draw on the outside may affect him later in the race as he would use more energy and ultimately run further trying to take an early the lead on the inside rail.

Identifying horses that perform well despite an disadvantageous draw is definitely worth considering when assessing pre-race form.

The Chester draw bias

Chester racecourse has a well-known draw bias thanks to the design of the course; a tight oval track with a short home straight.

Considering what we discussed above, this track is perfect to produce a draw bias, especially over five furlongs, where low draws have a considerable advantage.

Let’s see if the data backs up our point of lanes 1,2 and 3 holding an advantage over 5f races at Chester. The data we looked at covers 46 races from 27th September 2014- 10th June 2017.

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As you can see for the data above, 63% of winners over 5f at Chester came from stalls 1, 2 and 3. As mentioned earlier this is because, over a short race, horses drawn on the outside have to either cover more ground or use more energy to gain a desired early position - leaving it devoid of energy for the final sprint.

Interestingly only 24% of pre-race favourites won, while place markets saw 55% of all positions taken by horses in stalls 1,2 or 3 leaving plenty of opportunities to trade the markets and find value based on the draw bias.

Blindly backing stalls 1,2 and 3 with a £5 stake per horse would have returned you a loss of £66 after Smarkets’s industry-low commission was applied, while backing lanes 1 and 2 would have returned a loss of just £3. Interestingly, just backing stall 2 would have returned you a profit of £149.

However, such a basic approach is clearly open for improvement and we wouldn’t recommend betting on any outcome without considering other factors to reinforce your reasoning.

With this said there appears to be a clear draw bias at Chester, and horses in stalls 1, 2 and 3 may be undervalued by the markets.

How the draw bias can create trading opportunities

We now know the draw can create betting opportunities and in some cases can result in a profit with a blind back strategy based on the stall numbers. Using the data available to your advantage you can then trade the market using either a:

  • Back to lay strategy
  • Lay to back strategy

Using Chester as an example, we already know the distance and the track, so once you have researched the size of the field and the ground, you can identify the horse's history to match up with the course characteristics.

Once the draw has been made you can select the horses offering value and back them especially if they are drawn in 1, 2 or 3. Using a simple back to lay strategy, you would then trade out once the horse's price drops.

A lay to back strategy is the reverse of the above, where you would capitalise on horses with a poor draw. You should consider the price of the horse, however, as too high and your risk will be substantial.

The data above showed that horses drawn above stalls 6 had only won 19% of the time, with stalls 10, 11 and 12 winning only 4% of races. Knowing that horses with a poor draw often struggle around Chester, you could lay them initially and if their odds worsen, back them to lock in a profit (sell high, buy low).

It’s important to note trading based on a draw bias is a long-term strategy, and your stake should take this into consideration.

Apply this to betting

When betting on the Flat season, whether you’re backing or laying, respecting the vital role the draw plays in the outcome of a race is key for profitable trading.

However, it is also imperative to couple this with further research such as the factors which can affect a draw bias, to find long-term value, and an edge, over the markets.  

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