The Weekend Tournament of the European Go Congress 2015 had 504 players in the list. It was a 5 rounds McMahon with the tiebreakers SOS-SOSOS, a supergroup of 24 players with a rating of at least 2542, a bar-1 group with ratings 2450-2541, a bar-2 group with ratings 2350-2449 etc, 0.5 points (rounded down) for missed rounds, pros called "8d", unknown-rated players getting default ratings (such as 2700 for 7d or 2600 for 6d, and those top Chinese players proved their strengths in this tournament) and AGA Rules.
In violation of the EGF General Tournament Rules §3.2.1 ("By default, players in the top groups of a tournament must play all rounds. In a McMahon tournament the top groups include any supergroups, the group above the bar, and the group just below the bar. A player starting in a top group may skip a round only in exceptional circumstances like a serious a medical problem proven by a doctor's certificate or a family member's decease."), top players were allowed to drop rounds. 8 players of the supergroup did so, usually as soon as their losses indicated that they could not compete for the top places any longer. For example, Remi Campagnie, Tanguy Le Calve and Benjamin Drean-Guenaizia dropped the tournament after their first round's loss. For a 5 rounds McMahon with SOS as the first tiebreaker, this is very bad for two reasons:
a) Dropping rounds greatly affects the order of the top players with 4 wins following the winner, who has 5 wins.
b) Other participants, who would have the intention to compete for top places seriously, are prevented from their chance because they cannot be in the supergroup (or top group) of limited size.
Such ought not to occur. Top players must play all their rounds seriously!
The top places were as follows, where "NA" means "number of opponents not playing all rounds":
Place Name Rk Co MMS Wins SOS NA
1 Kim, Young-Sam 7d KR 31 5 145 3
2 Dinerstein, Alexandre 8d RU 30 4 146 0
3 Chan, Yi-Tien 7d TW 30 4 144 3
4 Lisy, Pavol 8d SK 30 4 143 1
4=Ma, Bin 7d CN 30 4 143 0
The players sharing place 4 also had the same luck in the SOSOS lottery (drawing the number 714). The relative order of the first two places was decided by their mutual game in round 5. The relative order of places 2 to 5 (the shared place 4) or, had Dinerstein beaten Kim, of the other group of top 4 wins players was decided as much by opponents missing rounds (and the tournament organisers allowing this at all) as by the tournament-strengths of the opponents performed in their played games.
Young-Sam Kim is well known at European Go Congresses. Surprisingly, there were no other Korean 7d competitors this year. Kim's tournament win could have been predicted by his rating 2791 while the second-highest rating at the start of the tournament was only 2711.
Players below the top with 4 or 5 wins:
UA 8 (of which are two win 5 wins)
XY 1 (9 other countries)
Among those with many such players and not too many participants, there are, you guess it, CZ 13, FR 9, UA 8. The same countries (apparently) relying on the EGF rating system to set ranks and therefore conservative ratings. (Poland had only 10 below-top players in this tournament and this may explain why its players did not score exceptionally.)
The bar-1 group consisted mostly of 5d players and two 6d, who did not show their greater strength in this tournament. The bar-2 group consisted mostly of 4d players with these rating exceptions:
Place Name Rk Co MMS Wins
29 Jasiek, Robert 5d DE 28 4
30 Cheburakhov, Andrej 5d RU 28 4
50 Rehm, Robert 5d NL 27 3
56 Halchenko, Mykhailo 5d UA 27 3
85 Shakhov, Kim 3d RU 26 2
I am not surprised by players #29 (who, on the Friday evening before the weekend tournament, got rid of his cold affecting his play and, e.g., two 1/2-point-like losses during the first week of the Main Tournament) and #30 but #56 was stronger a couple of years ago. IOW, the ratings' wisdom does not in general exceed the players' knowledge about their own strength expressed in their self-declared rank. All we can say about ratings below the very top players is that there is some good correlation on average (although maybe shifted by 1/2 or 1 rank in countries with self-declared ranks). However, for the bar-3 group and below, the correlation is much weaker because various ranks can be found within a range of 100 rating points.
Does using ratings for forming McMahon groups provide an advantage or disadvantage compared to not using ratings at most other congresses (i.e. except for Bordeaux)? Neither removes the rank difference of ca. 1 between countries not using versus using the rating system. Neither avoids exceptional players finding themselves in the wrong start McMahon groups. Which system (self-ranking or rating) is better cannot be answered easily, but IMO a combination of both systems applied carefully on a per-player basis might reduce the number of exceptions. However, for big tournaments with several hundred players, such would require meticulous organisational preparation.
Oh - my losses in round 5 and in the 9x9 KO stage against Mateusz Surma: I had not seen his play before, but now I understand why he could become an EGF professional. He has a very profound knowledge and calmly assesses every position's aspects. His play is not flawless but he ensures to let his mistakes impact a game less than his opponent's. In the 9x9 game, he won mainly because he demonstrated that one should not make an arbitrary second black move of the game but choose it after considering the best replies.http://egc2015.cz/results/wallweek