Backgammon Position #14 – The Gammon Factor

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This position is a typical blitz. White has been aggressively attacking black who now finds himself on the bar facing a four-point home board. White doubles. Should Black take the double?

Let us evaluate by using our four basic criteria:

The Race: – black trails by 13 pips in a long race. Black has chances of winning the race.

Position: – White has the better home board but black has only one checker back to white’s two. Black’s position is a little inflexible and having a third checker out of play on his 3-pt certainly does not help. I would estimate the position element as being the same for both players.

Threat: – White’s big threat is to close black out and then black will not be able to move again until the bear-off. On the other hand black threatens to escape his back checker when it will be white who has to escape his men. White’s threat is immediate and obvious so advantage to white.

Opponent: – In this sort of position it does help to know your opponent. Will he play the blitz aggressively? Does he understand the blitz? If he is a cautious player you have more room to take.

Overall then, advantage to white and certainly a double as the position is highly volatile. Can black take the double?

The answer is no and the reason is that when black loses, over 40% of the time that he does so, he will lose a gammon and four points. He will win more than the 25% of time but he doesn’t win often enough to offset the gammon losses.

Luckily there is a rule of thumb for these gammonish positions

Divide your expected gammon loss by 2 and add the figure to the “normal” take percentage of 25%. So if you expect to lose a gammon 20% of the time (i.e. when you lose the game one fifth of those losses will be gammons) then add 10% to the 25% to give 35%. If you can win the game 35% of the time then you can take otherwise you have to drop.

As you can see from the rollout data below black can win from this position about 30% of the time but he loses a gammon about 43% of the time (31.9 expressed as a percentage of 70.3). We can see that Black is nowhere near a take and he must pass the double. Many would be deceived by the closeness of the race and black’s sound structure and take but that would be to overlook the key to the position – the gammon rate!

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This article only looks at the very basics of the gammon factor – we will take a more detailed look in subsequent articles.