Nếu bạn chơi trò chơi tới điểm, trong đó bạn phải thắng 2 , bạn có thể cho rằng người chơi chơi 6 điểm. Nếu không có người chơi nào thắng 2 , thì điểm số được gắn 3 - 3 , và sau đó bạn chơi các cặp điểm cho đến khi một người chơi thắng cả hai. Điều này có nghĩa là cơ hội để thắng một trò chơi tới 4 điểm, khi cơ hội của bạn để giành được mỗi điểm là p , là4223−34p
.
p6+6p5(1−p)+15p4(1−p)2+20p3(1−p)3p2p2+(1−p)2
Trong trò chơi nam cấp cao nhất, có thể là khoảng 0,65 cho máy chủ. (Sẽ là 0,66 nếu nam giới không dễ dàng trong lần giao bóng thứ hai.) Theo công thức này, cơ hội giữ giao bóng là khoảng 82,96 % .p0.650.6682.96%
Giả sử bạn đang chơi tiebreaker tới điểm. Bạn có thể giả định rằng các điểm được chơi theo cặp trong đó mỗi người chơi phục vụ một trong mỗi cặp. Ai phục vụ đầu tiên không quan trọng. Bạn có thể giả sử các cầu thủ chơi 12 điểm. Nếu họ bị ràng buộc tại thời điểm đó, thì họ chơi cặp cho đến khi một người chơi thắng cả hai cặp, điều đó có nghĩa là cơ hội có điều kiện để giành chiến thắng là p s p r / ( p s p r + ( 1 - p s ) ( 1 - p r ) ) . Nếu tôi tính toán chính xác, cơ hội để thắng một tiebreaker thành 7712pspr/(pspr+(1−ps)(1−pr))7 điểm là
6p6rps+90p5rp2s−105p6rp2s+300p4rp3s−840p5rp3s+560p6rp3s+300p3rp4s−1575p4rp4s+2520p5rp4s−1260p6rp4s+90p2rp5s−840p3rp5s+2520p4rp5s−3024p5rp5s+1260p6rp5s+6prp6s−105p2rp6s+560p3rp6s−1260p4rp6s+1260p5rp6s−462p6rp6s+prpsprps+(1−pr)(1−ps)(p6r+36p5rps−42p6rps+225p4rp2s−630p5rp2s+420p6rp2s+400p3rp3s−2100p4rp3s+3360p5rp3s−1680p6rp3s+225p2rp4s−2100p3rp4s+6300p4rp4s−7560p5rp4s+3150p6rp4s+36prp5s−630p2rp5s+3360p3rp5s−7560p4rp5s+7560p5rp5s−2772p6rp5s+p6s−42prp6s+420p2rp6s−1680p3rp6s+3150p4rp6s−2772p5rp6s+924p6rp6s)
If ps=0.65,pr=0.36 then the chance to win the tie-breaker is about 51.67%.
Next, consider a set. It doesn't matter who serves first, which is convenient because otherwise we would have to consider winning the set while having the serve next versys winning the set without keeping the serve. To win a set to 6 games, you can imagine that 10 games are played first. If the score is tied 5−5 then play 2 more games. If those do not determine the winner, then play a tie-breaker, or in the fifth set just repeat playing pairs of games. Let ph be the probability of holding serve, and let pb be the probability of breaking your opponent's serve, which may be calculated above from the probability to win a game. The chance to win a set without a tiebreak follows the same basic formula as the chance to win a tie-breaker, except that we are playing to 6 games instead of to 7 points, and we replace ps by ph and pr by pb.
The conditional chance to win a fifth set (a set with no tie-breaker) with ps=0.65 and pr=0.36 is 53.59%.
The chance to win a set with a tie-breaker with ps=0.65 and pr=0.36 is 53.30%.
The chance to win a best of 5 sets match, with no tie-breaker in the fifth set, with ps=0.65 and pr=0.36 is 56.28%.
So, for these win rates, how many games would there have to be in one set for it to have the same discriminatory power? With ps=0.65,pr=0.36, you win a set to 24 games with the usual tiebreaker 56.22%, and you win a set to 25 game with a tie-breaker possible 56.34% of the time. With no tie-breaker, the chance to win a normal match is between sets of length 23 and 24. If you simply play one big tie-breaker, the chance to win a tie-breaker of length 113 is 56.27% and of length 114 is 56.29%.
This suggests that playing one giant set is not more efficient than a best of 5 matches, but playing one giant tie-breaker would be more efficient, at least for closely matched competitors who have an advantage serving.
Here is an excerpt from my March 2013 GammonVillage column, "Game, Set, and Match." I considered coin flips with a fixed advantage (51%) and asked whether it is more efficient to play one big match or a series of shorter matches:
... If a best of three is less efficient than a single long match, we
might expect a best of five to be worse. You win a best of five 13
point matches with probability 57.51%, very close to the chance to win
a single match to 45. The average number of matches in a best of five
is 4.115, so the average number of games is 4.115×21.96=90.37. Of
course this is more than the maximum number of games possible in a
match to 45, and the average is 82.35. It looks like a longer series
of matches is even less efficient.
How about another level, a best of three series of best of three
matches to 13? Since each series would be like a match to 29, this
series of series would be like a best of three matches to 29, only
less efficient, and one long match would be better than that. So, one
long match would be more efficient than a series of series.
What makes a series of matches less efficient than one long match?
Consider these as statistical tests for collecting evidence to decide
which player is stronger. In a best of three matches, you can lose a
series with scores of 13−7 12−13 11−13. This means you would win 36
games to your opponent's 33, but your opponent would win the series.
If you toss a coin and get 36 heads and 33 tails, you have evidence
that heads is more likely than tails, not that tails is more likely
than heads. So, a best of three matches is inefficient because it
wastes information. A series of matches requires more data on average
because it sometimes awards victory to the player who has won fewer
games.