: Re: ((no subject))
(2005-12-14 15:21) [#743]
you assume a handicap (black, no komi).
If you are one stone weaker than your opponent, then taking black without komi should give a 50% chance to win (since you are, in effect, playing equally after handicap). This is not necessarily true for the weaker player where 6 stones often doesn't make much of a difference.
Playing equally, the player who is one stone stronger in rank should win approximately 4/5 of the matches. Weaker ranks usually have higher standard deviation but aside from that the approximation should still hold.
Using komi also assumes that games go into the endgame. This is not the common case however - it is much easier to use a handicap stone than the extra komi.
: Re: winning percentages if taking Black without komi
(2005-12-15 14:55) [#744]
1 rank difference is usually set to 1 stone difference if playing handicap.
If not using handicap, there is (seems to be) a a correlation
of winning p=67% (don't nail me on that value, it can be different) of games against a player one stone weaker (if not equalized by handicap and/or komi).
When using the ELO ranking system (please check out the original article at gobase or at the EGF site), this winning expectancy is compared with the actual results and players get awarded points added/deducted according to the probability of their results. (Each) delta = 100 points difference should then relate to
a winning probability of p (resp. 1-p) and in an ideal world - (each one) grade difference in rank.
The ideal world is somewhat distorted (50 ELO points?) by Black starting even games and GIVING komi, while White starting handicap games and NOT GIVING komi (advantageous).
Hence, one will get skewing, kurtosis at bigger delta and some swivelling distortion at delta = +/-0.
Because this affects all players, which is a big number, tournaments are usually played on even, few tournaments are ONLY played with handicap, the whole system functions (seems to be stable, no known de-/in-flation know to me). Furthermore at delta >= 900, everything can happen.
83% seems to be more the equivalent of a 2-stone handicap.
"5 out of 6 games against someone my level, if only they give me Black with no komi." This sounds like 1/2 (one half or 0.5) handicap, if the other one has the same strength.
If the relation was linear (I guess it's not),
if a 1-stone handicap gives a winning percentage of 67%,
then 0.5 stone handicap => 58.5% which means I would bet more (and safer) on (100%/8.5% = 1/12) on 7 games out of 12,
resp. 7:5 (esp. if we are not pros).
NB: (several days later) I am not sure anymore wether "Black with no komi" is 0.5 handicap, if the other one has the same strength, it might be in fact 1.0 handicap.
That'd change the calculation to 67%/100% =ca. 4 out of 6.