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Number of games necessary to get approx PR
Posted By: Bob Koca
Date: Tuesday, 11 February 2014, at 9:41 p.m.
In Response To: Number of games necessary to get approx PR (eXtreme Gammon)
"This is based on STDEV of 8.16 for my unlimited games (4000 games, overall PR of 5.5)."
The 1.6 value was obtained as: The sample STDEV of 100 games is then 8.16/ SQRT(100) = .816. Multiplying by 1.96 gives the approximate + 1.6 value.
I think that technique is faulty and significantly overvalues the size of the confidence interval. The problem is that the average PR is per decision and not per game. There will occasionally be games that have a very high PR and I think those games will tend to be the short ones. The PR from that game thus does not count as much as a typical length game.

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