Investigating “The Bigger the Field, the Better the Favourite” Theory

This adage suggests that it is profitable in the long-term to back a reasonably short-priced favourite in a big field. It is a theory that makes sense in many ways. First of all, if there are 12+ runners and one horse is a clear market leader, it stands to reason that it is a particularly strong horse to be priced as such amid a bigger field.


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There is also the tendency of races with bigger fields to be more “truly-run” events than those with smaller fields. Races with smaller fields tend to have no discernible early pace or cover for any runners in need. In such affairs, a front-running favourite could be left badly exposed, which is something less likely to happen in bigger fields.

Finally, races with more runners are usually far less competitive than one might assume. Overall, around 85% of horses in the top five in the betting market win the race. In races with 12 runners, this figure drops to 71.57%. In races with 16+ runners, 58% of races are still won by horses in the top five of the betting market.

In all UK races since the beginning of 2014, 35.25% of favourites win the race. The win rate will obviously drop as the field gets bigger, but 26.49% win in races with 12+ runners and 20.15% win in races with 16+ runners.

The difference between favourites in 12 and 16 runners is not surprising at first glance, but it makes less sense when you realize that races with large fields routinely feature horses with no realistic shot of winning. For instance, while horses at SP odds of 20/1 have won 15.56% of all races with 16+ runners since the start of 2014, there are several such horses in each race. Overall, only 1.73% of all 20/1+ entries have triumphed in a race.

Favourites in Races with 16+ Runners

First of all, I have elected to focus on races with 16 or more runners first. For the record, all figures are from the beginning of 2014 to the end of July 2018 unless otherwise stated.

Here is how ALL clear favourites in ALL UK races with 16+ runners fare:

BetsWinsStrike RateROI (BF)
1,21124420.15%-8.93%

This looks pretty grim initially. It is a low strike rate, and a loss of almost 9% is crippling. However, we are looking for horses at relatively short odds so let’s take a look at favourites that set off at 9/4 SP (3.25) or less.

BetsWinsStrike RateROI (BF)
2427631.41%-19.58%

Although the win rate rises significantly as expected, the loss is even worse at almost 20% on Betfair and 22.97% off the SP.

Things are only marginally better for odds-on favourites:

BetsWinsStrike RateROI (BF)
392051.28%-11.3%

The SP loss is 13.69% by the way, and the above is a tiny sample size. It is better to focus on handicap races, but even then, you are still suffering a loss.

Favourites in Races with 12-15 Runners

In the introduction, we saw that favourites in fields with 12+ runners had a reasonable win rate of over 26%. Given the poor results in races with 16 or more horses, it stands to reason that events with 12-15 runners may offer a glint of light. Here is the performance of ALL clear favourites in such races:

BetsWinsStrike RateROI (BF)
6,5441,81027.66%-3.1%

We are still suffering a loss, but there is much more to work with. Once again, let’s check out horses at SP odds of 9/4 or less:

BetsWinsStrike RateROI (BF)
2,6021,00938.78%-1.63%

Finally, let’s check out odds-on favourites:

BetsWinsStrike RateROI (BF)
41623756.79%-3.21%

There is possible value in looking at horses at 9/4 or less with a strike rate approaching 40% and a miniscule loss.

Next, I checked horses at 9/4 or less in handicap races only:

BetsWinsStrike RateROI (BF)
1,15840735.15%-0.03%

You are effectively breaking even here although SP losses are 4.34%.

Of the three codes, National Hunt is by far the best option:

BetsWinsStrike RateROI (BF)
26511041.51%19.57%

A profit of almost 20% is always welcome, and you would have profited in three of the last five years.

Eliminating Non-Contenders & Final Thoughts

You will typically find a couple of races a day that fit most of the criteria. Remember, you ideally want NH races with 12+ runners and a clear favourite with odds of 9/4 or less. When you remember what I said about 20/1+ shots, you can safely remove close to half the field in a lot of events!

For example, horse #7 could be running his first handicap while horse #8 is with a new trainer. Perhaps another remaining contender is a C&D winner but is completely out of form, while yet another possible winner has no wins in eight career races and is unlikely to break his duck today.

At this stage, you have to ask if the horse in question is a worthy favourite and whether the remaining contenders have a chance. In a lot of races, you will find at least one dangerous contender; maybe it has won a couple of races recently over the same distance for example.

There will even be occasions where you end up backing an entirely different horse to your original plan because it represents far better value! However, if you believe the favourite is still value at odds such as 6/4, put your money where your mouth is and have faith in your selection process.

Overall, we’ve found the “bigger the field the better the favourite” theory doesn’t hold much water, especially in extra-large fields of 16+ runners. You will have the greatest success focusing on National Hunt races with 12-15 runners, but even then, it should be a case of determining if the horse is a worthy favourite, or is likely to get defeated, rather than blindly backing it.