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eXtreme Gammon question

Posted By: Bob Koca
Date: Thursday, 27 August 2009, at 4:08 a.m.

In Response To: eXtreme Gammon question (Timothy Chow)

"Your point is that it would have been more precise for me to say, "If I declare the higher-scoring play to be the better play, what percentage of the time will I be correct, assuming that the DMP winning probabilities of the two plays are picked uniformly at random?" I agree that I was making that implicit assumption. With that assumption, though, what I said was correct. "

I still disagree. Let's say it is DMP and there are just two candidate plays. The statement "play A is better than play B with 95% confidence" means that if the plays were actually equal that the diffence in the rolled out values would only be that large or larger 5% of the time. This is not the same as saying there is a 95% chance that A is the better play.

For example some rollouts will involve situation where we believe one play to be superior. The RO quickly reaches 95% confidence. We then are quite sure it is correct (certainly more than 95%). For example what do you think the chance is that for an opening 31 that making the 5 point is better than splitting. You may be 99.9999% sure that it is. But if you do the following RO you don't want to change your answer to only about 99% (based on the 2.4 JSDs) do you? Your technique of asserting the best play based on a 95% confidence RO actually gets it right more than 95% of the time.

The score (after 0 games) is: gnubg 0, user 0 (match to 7 points)

Move number 2: user to play 13

gnubg167


2O ' ' ' '5X '3X ' ' '5O

2X ' ' ' '5O '3O ' ' '5X

user167

Position ID: 4HPwATDgc/ABMA Match ID: cInsAAAAAAAA

# Ply Move Equity
  1 R 8/5 6/5 +0.201383
 
0.5453110.1650970.007538-0.4546890.1201230.006558 +0.140008 +0.201383
0.0056760.0052570.002001-0.0056760.0040810.000945 0.014320 0.035540
 
  Full cubeful rollout with var.redn.  
  134 games, Mersenne Twister dice gen. with seed 867982123 and quasi-random dice  
  Stop when best play is enough JSDs ahead: limit 3.2 (min. 324 games)  
  Play: 0-ply cubeful [expert]  
  Cube: 0-ply cubeful [expert]  
  2 R 24/23 13/10 +0.055182 ( -0.146201)
 
0.5056780.1410830.004905-0.4943220.1319180.005682 +0.017300 +0.055182
0.0062550.0062350.001534-0.0062550.0048080.001114 0.018588 0.045499
 
  Full cubeful rollout with var.redn.  
  133 games, Mersenne Twister dice gen. with seed 867982123 and quasi-random dice  
  Stop when best play is enough JSDs ahead: limit 3.2 (min. 324 games)  
  Play: 0-ply cubeful [expert]  
  Cube: 0-ply cubeful [expert]  
  3 0 13/9 -0.001933 ( -0.203316)
  0.496628 0.145331 0.007383 - 0.503372 0.139005 0.006489  
  4 0 13/10 6/5 -0.003447 ( -0.204830)
  0.500172 0.145310 0.008305 - 0.499828 0.148288 0.008802  
  5 0 24/20 -0.005912 ( -0.207295)
  0.500101 0.125114 0.005943 - 0.499899 0.132557 0.003575  

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