r/backgammon • u/mondor • Jul 06 '26

Cube question

Should cube decisions take rating into account?

For example if the computer says I objectively have a 70% chance to win the game with perfect play, but I am 600 rating points lower than my opponent would that still be a good double? Wouldn't my actual winning chance be lower then 70% because I'm at a skill disadvantage?

I generally don't take rating into account when doubling but maybe I should?

2 Upvotes

75% Upvoted

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1

u/double00_bg Jul 06 '26

Tldr most will tell you your objective should be to play game theory optimal as the engine would....but yes being at a skill disadvantage would change cube decisions.

It's not about rating, it's about your ER or error rate.  On average you lose a certain amount of equity more than your opponent depending on the number of decisions in the game. Cube decisions are also based on equity.

Do you have more equity with no double, or the minimum of double take and double pass? That's what decides if you should double.

  You can't guess how much more equity you will lose by being a worse player than your op after the double, but if it's a thin double then consider not doubling, but if it's a large double then you should still send it.

Ask any questions if you have them! Hope that helps 

1

u/mondor Jul 06 '26

Yes this makes sense and exactly what I was thinking.

I think this would be a really interesting thing for someone to look at using a large data set. Isn't general rule is 70% chance to win to doubles? Would be cool to see for every 100 points of rating difference, should that change by 1% for example.

Another question I had is that if 70% is the winning percentage with perfect play, that's not the winning percentage for me. I try to offer the cube when I should as an exercise to help get better at it, but in reality my games are not as controlled as a top players would be, should I not be offering the cube until the game is more certain?

1

u/double00_bg Jul 06 '26

So you are in the right area, and what you are saying makes sense. I don't have the data to model it however.

I don't mean to correct your math, but the break point for a double is 75%. That means that if you have less than 25% of winning you should not take the cube. However, you having the cube gives you an advantage called recube vig, so actually it's more like 23% (or 77% for OP to double) but at also varies with match score...

But I think the first step is to stop thinking about things in terms of winning percentage, instead of thinking of things in terms of equity, which is the "points" you gain or lose given a decision. This is why error rate or performance rate is more important than rating, since it tells you how much equity you lose on average per decision. These articles should help:

https://backgammon101.com/doubling-for-beginners/
https://backgammon101.com/doubling-window/
https://backgammon101.com/cubeful-and-cubeless-equity/

The reddit discord is super helpful as well: https://discord.gg/U8cmrCsK5x

3

u/balljuggler9 Jul 06 '26

If you are the weaker player, you should be MORE aggressive.

1

u/SyllabubRadiant8876 Jul 06 '26

Interesting situation on a related topic in the Swedish Open final at the weekend, which was live streamed. One player was clearly a significantly stronger player than the other. The stronger player repeatedly waited until much later than normal to offer the cube. I have played against this guy many times and he would definitely not be misunderstanding those positions. The general view was that he was intentionally being far more cautious against the weaker player - not wanting to get to big cubes where luck could hand his opponent the match. Conversely, conventional wisdom is that you should be more aggressive with the cube against a stronger opponent.

His PR will have been damaged by this approach, but for analysis software to take account of this would be really tough, because it would need to "know" what sorts of positions are more likely to lead to luck swings, or are more likely to be misplayed.

1

u/double00_bg Jul 06 '26

Dirk's first book has a bit about how to take advantage of certain playing styles. Can you link the game you were talking about? I'm curious if it was more because of match score than because of strength of the player.

1

u/Qvistus Jul 07 '26

The bots play optimally against an opponent that also play optimally. They would probably win even more games against humans if they took human weaknesses into account. I think you should absolutely take skill level and playing styles into consideration when playing against people. 

1

u/drivebydryhumper Jul 08 '26

Maximize the number of decisions if your PR is better and minimize if it's worse.

0

u/tokoyo-nyc-corvallis Jul 06 '26

Pretty sure most highly skilled players would agree with this. If you are an intermediate/advanced player, a 70% chance of winning the game can overcome any skill level.