# Steamers and Drifters: Part 2

In this follow-up article I am once again looking at market movement between the bookmaker’s opening show and the returned Starting Price, * writes Dave Renham*. The data I've used has been taken from 2018 to 2022 for all UK flat and all-weather racing. Bookmaker data is taken from William Hill.

In the first piece, which you can read here, the overall stats showed that a bigger percentage of horses drift (lengthen) in price from their opening price than shorten, when comparing market movement from opening show to SP. The biggest difference can be seen in horses that open 10/1 or bigger; of these over 42% drift in price compared with 29% that shorten.

Up to now in this research, I have not considered how much the price changed. Clearly all price movement is not the same; for example, a horse can drift from 4/1 to 9/2, but another 4/1 shot could drift far more dramatically out to 10/1 as an extreme, but perfectly credible, example. Likewise, horses that shorten in price can vary markedly in terms of how much their price contracts.

At this point I want to discuss what I mean by "significant price changes" as we need to be clear that looking at the difference in two prices does not necessarily tell the whole story. To help explain what I mean, let me give you some context. Let us consider two horses:

Horse A – whose opening price is 40/1 and whose SP is 20/1

Horse B – whose opening price is 6/4 and whose SP is Evens

If we focus solely on the prices, Horse A has shortened more because 40/1 to 20/1 is a 20-point truncation, whereas for Horse B moving from 6/4 to Evens is only a 0.5-point move. However, in terms of the chance of winning, Horse B has actually improved its chances more. In order to appreciate this, we need to understand the percentages behind the odds – in other words the percentage chance of winning according to the odds. The table below illustrates this:

As the table shows, Horse A has improved its chances of winning by 2.4% (4.8% minus 2.4%). However, Horse B has improved its chance of winning by 10% (50% minus 40%). Knowing and understanding betting odds in terms of the percentage chance of winning is very important. When I wrote my article on trying to create an odds line, the percentage chance for each horse was something I touched upon. Without it, you cannot easily create an accurate odds line.

*At the end of this article, I have produced a table with fractional odds, decimal odds and the implied probability (percentage chance of winning) for betting prices. Readers, if required, may use it as a ready reckoner to convert odds into percentages.*

It is now time to compare horses that shorten considerably from opening show to SP with those that lengthen/drift considerably. I am going to only consider horses whose prices have changed, in win percentage terms, by 10% or more. Hence the 6/4 to Even money horses mentioned earlier will count, but not the 40/1 into 20/1 ones. (N.B. The word ‘steamer’ is often used about a horse whose price starts to drop dramatically so for the rest of the article I will use ‘steamer’ for horses that shorten in price).

Let's look at strike rates first – for horses whose win chance changes by 10% or more due to their odds move:

These figures correlate with the findings of the first article and the general data set. Steamers have won 5.5% more often than drifters. However, this does not mean that steamers have produced better returns. In fact, it is quite the contrary as the graph below shows:

These strong steamers actually lost over 13 pence in the £ betting to Betfair SP; drifters lost just 1p in the £. The full breakdown of the results is as follows:

A 10%+ change in win percentage between opening odds and SP only occurs roughly once a day on average. Hence, this type of percentage movement can be considered a major price change.

I thought it might be interesting to breakdown the results further by splitting them by the odds at which they opened. Here are the stats for the * steamers*:

I have tried to group them so that the number of runs for each group is similar. What seems to be clear is that the worst performing steamers from a profit/returns perspective were those that opened at 11/2 or bigger. The shorter prices of 6/4 or shorter also fared relatively poorly.

Onto * drifters *now. There are not many big prices here because a 10%-win probability movement is impossible for horses priced 9/1 or bigger. For an extreme example to illustrate this, a horse drifting from 9/1 (10% chance) to 1000/1 (0.1% chance) has a win probability price movement of only 9.9%:

The results for drifters are more consistent in terms of profits/returns – there is very little difference between the worst performing price band and the best one.

It is clear from this data that if betting at BSP, significant drifters are better value than significant steamers.

**Trainers**

It is not worth looking at individual trainer data for the strength of steamer/drifter (+ / - 10%), as the sample sizes are going to be too small. Therefore, I am going to focus on trainer data for those horses whose prices changed in win probability terms by 5% or more, rather than 10%. This would include, for example, a horse shortening from 8/1 to 5/1, or one drifting from 6/1 to 10/1. I also restricted the runners a little by looking at horses that opened in price between Evens and 50/1. I ignored odds-on runners and those priced 66/1 or bigger for two reasons: firstly, because the majority of punters do not bet in these price brackets and, secondly, the individual trainer sample sizes are extremely small.

** Steamers** - As noted above I have broken down trainer performance where the win probability implied from opening odds to SP has improved by 5% or more. Trainers with at least 100 qualifying runners are listed. They are ordered by strike rate/win percentage:

The strike rates are decent as you might expect for steamers, but only a handful of trainers have made a profit. The Johnston and Channon stables have both done well from a profit perspective, as has Mick Appleby. Of course, for steamers, any value is gradually diminishing as the price is contracting.

Ten trainers have produced losses of more than 20 pence in the £, which is quite significant especially considering we are using BSP. The Crisford stable has the worst returns, edging above 30% for their losses.

Of course, if you could predict the steamer before it started shortening in price, and bet before it moves markedly, then the likelihood is that most of the trainers in the list would become profitable. Unfortunately, none of us has a crystal ball, which makes those types of predictions somewhat tricky! What would be interesting to find out is what percentage of horses that initially shorten from opening show, continue to shorten. Likewise, it would be really useful to know what percentage of horses that initially drift from opening show continue to drift. However, I do not have that information and guess the only way to find out would be by doing a live day by day data gathering exercise. That’s for another lifetime!

** Drifters** – Switching to drifters now below is a table of trainer performance where the win probability change from opening odds to SP has decreased by 5% or more. Trainers with at least 100 qualifying runners are once again listed.

There are six trainers in profit here with Stoute, Haggas and Balding drifters performing particularly well from a returns and strike rate perspective. Indeed, all trainers in the above table have combined to secure a small profit of £21.52.

The two trainer tables I have shared indicate that at this 5%+ level of steam/drift, bettors might be better off backing drifters rather than steamers. In fact, if we look ALL trainers as a whole for both groups, we get the following overall figures:

Steamers, as we have come to expect, have the better strike rate, but drifters are offering punters much better value. So, the question is, do you want more chance of winners, or more chance of a profit?

Going back to the stats for Sir Michael Stoute in the second table above, his non-handicap drifters have totally outperformed his handicap drifters as the chart below shows:

Strike rates are similar but there is a big difference in the profits. Non-handicap drifters of this strength (5%+) would have secured Stoute followers impressive returns of 70 pence in the £ to BSP.

I must admit this has been a very interesting area to research. It is something I have looked at before but not in as much detail. It may be worthwhile comparing early morning odds to SP odds in a future piece, and also at some point I should see if the patterns I have found in these two articles correlate with National Hunt data. Anyway, as ever, I hope you have found the research enlightening, and all comments are appreciated as it helps me with my future work.

- **DR**

p.s. here is the table I mentioned earlier with fractional odds, decimal odds and the implied probability (percentage chance of winning) for betting prices.

Fractional Odds |
Decimal Odds |
Implied probability (% chance) |

1/100 | 1.01 | 99% |

1/5 | 1.2 | 83.3% |

2/9 | 1.22 | 81.8% |

1/4 | 1.25 | 80% |

2/7 | 1.29 | 77.8% |

3/10 | 1.3 | 76.9% |

1/3 | 1.33 | 75% |

4/11 | 1.36 | 73.3% |

2/5 | 1.4 | 71.4% |

4/9 | 1.44 | 69.2% |

1/2 | 1.5 | 66.7% |

8/15 | 1.53 | 65.2% |

4/7 | 1.57 | 63.6% |

8/13 | 1.62 | 61.9% |

4/6 | 1.67 | 60% |

8/11 | 1.73 | 57.9% |

4/5 | 1.8 | 55.6% |

5/6 | 1.83 | 54.5% |

10/11 | 1.91 | 52.4% |

Evens | 2 | 50% |

21/20 | 2.05 | 48.8% |

11/10 | 2.1 | 47.6% |

23/20 | 2.15 | 46.5% |

6/5 | 2.2 | 45.5% |

5/4 | 2.25 | 44.4% |

11/8 | 2.38 | 42.1% |

7/5 | 2.4 | 41.7% |

6/4 | 2.5 | 40% |

8/5 | 2.6 | 38.5% |

13/8 | 2.62 | 38.1% |

7/4 | 2.75 | 36.4% |

9/5 | 2.8 | 35.7% |

15/8 | 2.88 | 34.8% |

2/1 | 3 | 33.3% |

11/5 | 3.2 | 31.2% |

9/4 | 3.25 | 30.8% |

12/5 | 3.4 | 29.4% |

5/2 | 3.5 | 28.6% |

13/5 | 3.6 | 27.8% |

11/4 | 3.75 | 26.7% |

3/1 | 4 | 25% |

16/5 | 4.2 | 23.8% |

10/3 | 4.33 | 23.1% |

7/2 | 4.5 | 22.2% |

4/1 | 5 | 20% |

9/2 | 5.5 | 18.2% |

5/1 | 6 | 16.7% |

11/2 | 6.5 | 15.4% |

6/1 | 7 | 14.3% |

13/2 | 7.5 | 13.3% |

7/1 | 8 | 12.5% |

15/2 | 8.5 | 11.8% |

8/1 | 9 | 11.1% |

9/1 | 10 | 10% |

10/1 | 11 | 9.1% |

11/1 | 12 | 8.3% |

12/1 | 13 | 7.7% |

13/1 | 14 | 7.1% |

14/1 | 15 | 6.7% |

15/1 | 16 | 6.2% |

16/1 | 17 | 5.9% |

18/1 | 19 | 5.3% |

20/1 | 21 | 4.8% |

25/1 | 26 | 3.8% |

33/1 | 34 | 2.9% |

50/1 | 51 | 2% |

66/1 | 67 | 1.5% |

100/1 | 101 | 1% |

1000/1 | 1001 | 0.1% |

Fascinating data as usual Dave,thanks for all your hard work !