The Checkout Combination Index explained

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December 1, 2016 by bsd987

I’ve been receiving a lot of questions about a metric I first mentioned a year ago but that I didn’t role out until two months ago: the Checkout Combination Index. Depending on how long you have been following me on Twitter, you may have seen that I’ve tracked eight different types of checkouts based on their difficulty.

First, there is the straight-forward situation where you have three-in-hand at a double. Phil Taylor comes to the board on, say, 32[1]. If he checks it out, I tick the box that says ‘made’; if he doesn’t, I tick ‘missed’[2]. As opposed to the checkout percentage that you may be aware of, I don’t care how many darts it takes. If Taylor goes inside on the first dart, misses outside double 8 on the second dart, and hits third dart, my statistics show him as 1/1, as if he hit the first dart. It doesn’t make a difference whether he uses all three darts or just one.

Second, there is the nearly as simple task as single-double. This includes any odd shot under 40 (e.g., 25 or 37), as well as 41 to 61 and 65. Since players almost exclusively go 25-D18 and 25-D20 from 61 and 65 respectively, I treat them as single-double outshots. I do so even when James Wade comes to the board and goes T7-D20. The mere fact that he goes a different route doesn’t change the type of outshot it typically is. And same as above, I don’t care if Gary Anderson takes out 25 1-D12 or 1-12-D6: It’s still a successful checkout.

The next two categories are a little bit more complicated. First, outshots of 62-64 and 66-80 are grouped together, as they can be done either single-single-double or treble-double (or, if you are Alan Norris on 80, double-double, much to Alan Warriner-Little’s disappointment). And second, outshots of 81-98 and 100 are grouped together. These are traditionally treble-double outs, although those between 81 and 95 can be altered through use of the bull. Players have more options here, and this category is a loose fit: a 96 out is noticeably more difficult than an 81. But subdividing this category would lead to smaller sample sizes and sometimes absurd statistics. So I’ve grouped them together, knowing that over time a player should have a roughly equal number of opportunities at both 96 and 81. Nonetheless, again, for both of these two categories, whether it takes two darts or three is immaterial: a checkout is a checkout is a checkout.

The fifth category—which historically we’ve associated with being James Wade’s and Simon Whitlock’s bread and butter—are those low three-dart outs that only require one treble to get to a double. The are outs of 99 and 101-120. Like before, some are clearly more difficult than others: 117 requires you to change trebles if you miss the first dart, whilst on 116 you can stay on the same treble you started on. But subdividing would again lead to absurdly small sample sizes. so I’ve grouped them together.

The sixth category are the fun potential bull finishes: treble-single-bull. They span from 121-130, as well as 132 and 135[3]. These are the last type of outshot where a player can recover from missing his first dart, at least so long as he hits the big number. There’s a small margin of error, and that margin affords the player a shot at the bull at the end. Yet again, I realize a 128 is harder than a 130: But the type of checkout is similar enough to group together.[4]

The last two categories are what Rod Studd would call the fanfare finishes. The penultimate category is treble-treble-double. These are outshots of 131, 133, 134, 136-158, and 160. These are hit about 5 percent of the time. And the final category are John Part’s big fishes: 161, 164, 167, and 170: treble-treble-bull. There isn’t much choice here[5]. These are about 2 percent outshots: they bring down the house for that reason.

Now, I’ve been tracking this data for a year, both from TV events and Euro Tour events. And for the top 40 or so players, I have a few hundred legs of data on how they’ve done on each shot. For some of the more fringe players, I have a small handful. But it creates a good mix. I now know that the PDC average with three-in-hand at a double is just less than 3-in-4 success rate, and even the best players miss about 20 percent of the time. You probably aren’t coming back to the board when Michael van Gerwen has three at D16, but you might. And it’s more often than you might think.

But still, missing three at D16 is worse than missing one at D16 for a 152: the result might be the same, but the probabilities of hitting when the visit started were far apart. If you’re an average professional, you had a 72 percent chance of taking out 32 in 3 darts. But you only had about a 5 percent chance of taking out 152. You were, in short, about 14-and-a-half times more likely to check out 32 than 152.

My index notices that, and it thus treats it accordingly. Misses at 32 hurt more than misses at 152, but successful 152 outshots count for more than successful 32 outshots[6]. From all these outshots, players are then indexed according to the PDC average (which does include BDO players at the Grand Slam) in each category. I then take into account the relative frequency with which each outshot finishes a leg. From this, I end up with 8 numbers—one for each outshot—which when added together give the Checkout Combination Index (CCI). A player who is the exact PDC average in all 8 outshots would have a rating of 100.00. A below-average player would be under 100; an above-average player would be above 100.

Let’s take a look at the ten players in the World Championships field who have the highest CCI:

Seed Player CCI Legs
12 Raymond van Barneveld 128.28 291.4
8 Mensur Suljovic 121.96 417.6
4 Phil Taylor 115.94 372.3
1 Michael van Gerwen 115.75 798.3
26 Justin Pipe 114.29 157.6
Darren Webster 113.59 222.4
6 James Wade 113.17 483.8
3 Peter Wright 112.47 671.7
13 Kim Huybrechts 111.64 305.5
22 Mervyn King 110.76 214.9

Most of those shouldn’t be a surprise. Barney’s finishing has been sublime the last two months. Like all my other statistics, I weigh more recent events more heavily, as well as TV events more heavily than Euro Tour events. Barney’s numbers from under 80—which weigh into the formula more than the other outshots—have been almost unbelievable. In his last 4 events (ET9, Grand Prix, Grand Slam, Players Championship Finals), Barney has successfully checked out 83.8% of the time with three at a double and 81.4% of the time on single-double outs. The PDC averages are 72.3% and 60.6% respectively. He’s also hit the third category of outs 55.7% of the time, while the PDC average is 45.2%. The fact that he doesn’t give you a chance on the outshots that are the most important to hit—as well as that he’s pretty good on the bigger outshots too)—makes him right now, by far, the best finisher in the game.

One problem with the index, which I plan to fix over the next year, is that right now I don’t consider pressure: there is a context difference between needing to check out 56 when your opponent is also on 56 than when he’s on 156 or even 256. Michael van Gerwen’s number is probably lower than it should be, as I’ve noticed (but not statistically tracked) a tendency for him to miss in clumps, but only when his opponent is far back. When the pressure is raised, van Gerwen rarely misses. If I were to add in an element that considers pressure, his rating probably would be a few points higher. This is something to consider going forward, but something I have not yet implemented.

Anyway, that’s how the CCI works. I’d be happy to answer most any question about it, although the exact formula is for me and me alone!

[1] I recognize that not all doubles are the same, especially when it comes to splitting doubles. However, it would be too small a sample size to treat D18 and D16 as two diferrent out-shots. The task is the same: take it out. Likewise, if a player chooses to split D19 and go 6-D16, I still consider it three-in-hand at a double: That he chose to alter it doesn’t change that he could have gone straight for it. Treating it differently creates problems, especially in the situation where he might only split second dart after blocking the double first dart. It’s cleaner to just group the outshot based on how it normally is taken out.


[2] Actually, I track this by old-fashioned pen and paper, so I make a dash in a column. But same difference.


[3] 121 and 125 could be done 25-treble-double, and some players—most notably Adrian Lewis and Raymond van Barneveld—very frequently take this approach. Nonetheless, I consider them to be treble-single-bull outs, regardless of the approach the player takes in the specific instance.


[4] Sometimes a player might treat one of these outs as a treble-treble-double out, especially if his opponent isn’t on a finish. For instance, Taylor might go T20 first dart as a 128 if Jelle Klaasen is on 216. Nevertheless, for the same reasons discussed in footnotes 1 and 3, I group all 128 outshots here. Same thing if Taylor goes 18-T20 and decides not to go for bull: it’s a missed 128 outshot.


[5] Like I said in footnote 3, if the player lays up, it still counts as a miss. Say Peter Wright needs 164 and hits two T19s, but realizing Stephen Bunting is back on 230, goes to S18 instead of bull to leave 32. I count it as a miss. The easiest reason for this is most of the time, Wright would have missed with one of the first two darts, and I’d be forced to guess whether he would have gone for bull with the third dart had he the chance. It’s simplest and cleanest to consider it a miss in all situations, even if the player chooses not to go for the bull.


[6] At least in direct appearances. If you think of a successful 32 outshot instead as the avoiding of a miss at 32, it helps you a lot, since missing 3 at 32 hurts you fairly significantly.




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