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Mini-manifesto on evils of PR gammon.

Posted By: Jason Lee
Date: Thursday, 28 May 2026, at 7:11 a.m.

In Response To: Mini-manifesto on evils of PR gammon. (Bob Koca)

UBK: The PR approach is not even needed at all. Variance can be reduced by just using variance reduced match win %ages which avoid almost all the issues of PR gammon. Nearly always would make the practical play to win the BACKGAMMON match.

I'm not going to push back on Bob's manifesto, because on the face of it, Bob is mostly right. But Bob has created a straw man argument.

The main benefit of PR is that it can be aggregated almost entirely independent of opponent. VRR cannot do this in a simple way. That is to say, when VRR says I was 57% to win a match, it matters A LOT who I played. When PR says I had a PR of 6 in a match, it matters very little who I played.

If your goal is to take two players and have them play against each other for 100 matches and decide who is the better backgammon player, it's UNQUESTIONABLY correct to use VRR. I will die on this hill. And if you think otherwise... I would refer to a quote from a friend I went to grad school with, who liked to say, "You're entitled to your opinion, no matter how wrong or stupid it might be.

If your goal is to take a bunch of players and look at 100 matches each, not in a round robin, but with somewhat arbitrary pairings (as would be the case if we just take a bunch of BMAB data) and against a very wide variety of opponents, and you want to decide who is the best backgammon player, VRR has a lot of problems that you're going to have to work out, and PR is a decent proxy.

Everything, whether VRR or PR, is subject to the whims of sample size problems.

By the way, I submit matches to BMAB, and I give a shit about my PR, only to the extent that it serves as a decent benchmark to my progress. Bob, if you can find a way for me to use VRR alone to benchmark my progress, I'm all ears. I don't think you can do it.

And yes, I play the ridiculous PR tricks that Stick served up at the beginning of the thread. I am not stupid enough to think that has ANYTHING to do with being a better player. I do a lot of stupid things in my life just for my own amusement.

JLee

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