Predicting pairings in a Swiss

Running Chess Tournaments
1

I’m in the middle of a tournament (2 games last weekend, 2 games this coming weekend), and I’m trying to predict who I’ll play in the next round, and with what colors. I think this is an easy one, so I’m mostly just using this scenario to increase my understanding of the inner workings of the Swiss system.

Here’s the situation: There are only 8 players, and it’s an Open Swiss. We’ll call the players 1 through 8, in order of ratings from highest to lowest. I’m 4.

First round pairings:
1 vs 5
6 vs 2
3 vs 7
8 vs 4

The higher rated player won every game in the first round, so pairings for the second round were straightforward:

4 vs 1
2 vs 3
5 vs 8
7 vs 6

I (player 4) scored an upset over player 1, making me the only person with 2 points after two rounds. 2 and 3 drew, so they both have 1.5. I actually don’t know what happened on the other two boards, but since they all lost in the first round, I know that none of those four players have more than 1 point.

So the questions are who will I play next round and with what color. Here’s my thinking: I (player 4) have 2 points, and there are two players with 1.5 points (players 2 and 3), so it’s logical to assume that the higher rated of those 2 (player 2) will be the one bumped up to the next score group to play against me. But player 2 and I both had black in the first round and white in the second round, so who will have which color if I play him? Or will I play against player 3 next, since he had white first round and black second round, so he and I could both keep alternating colors if I have black against him next?

–Fromper

2

It depends on how similar 2 and 3s ratings are. If they are close enough, the TD could switch them to keep the pairings on color like he did in the second round.

Alex Relyea

3

The TD had nothing to do with that. I don’t know what computer program he uses, but this TD always lets the computer decide the pairings. Occasionally, he’ll tell the computer to make an exception (such as to give himself the bye if there’s an odd number or to keep family members from getting stuck playing each other if there are other reasonable options), but mostly, it’s the computer program doing all the thinking.

–Fromper

4

It doesn’t matter whether a computer or a human TD makes the pairings. Either way, he/she/it is likely to transpose player 2 with player 3 to improve colors – if the rating difference between 2 and 3 is small enough (say, 80 points or less).

Transpositions to equalize color are supposed to be within 200 points. Transpositions to alternate color are supposed to be within 80 points. Here alternation is the issue, so a transposition of up to 80 points is acceptable.

However, some TD’s (whether human or silicon) may be reluctant to make a large transposition when two different score groups are involved. In this case it translates into a question of which player to consider the “odd player” in the 1.5 group. So the program may decide not to make this transposition.

It also depends on the colors in the remaining score groups. If transposing improves the colors in your pairing, but worsens them elsewhere, the transposition wouldn’t really accomplish anything, so if the TD (or program) is “looking ahead” properly, he/she/it probably wouldn’t do it.

Personally, in a larger tournament, I might make the transposition up to 80 points, unless the effect is merely to push the bad color down into a lower score group, in which case I wouldn’t transpose.

But in this case one should also consider the “small tournament” effect. With only 8 players, transpositions which merely alternate colors can be a bad idea. If, for example, all the colors alternate in the first three rounds, then each player will have only one possible opponent in round 4 who will continue to alternate colors – and that pairing would likely be far from ideal from a score standpoint.

Therefore, in this case I vote for NOT transposing.

We really need to see the whole wall chart – scores, ratings, and colors – for all the players, before there is much point in trying to predict anything.

Bill Smythe

5

Ok, suddenly, I don’t feel so stupid for not knowing what seemed like an easy question. :confused:

I don’t have the complete pairings and everything, but from what you said, it seems surprising that the program chose to pair 2 vs 3 and 4 vs 1 in the second round, since the rating difference between 2 and 3 is almost 300 points. Although now that I think about it, the rating difference between 1 and 2 is only around 30 points, and the rating diff between 3 and 4 is only about 50 points. So maybe that’s why it didn’t matter which of the two lower rated players were paired against which of the two higher rated players. Either way, there’d be a ratings difference of over 290 points between the players going against each other on both of the top two boards.

–Fromper

6

In round 1, the players being transposed were 3 and 4. Therefore, the rating difference between 3 and 4 is the relevant one, not the difference between 2 and 3. The difference between 1 and 2, the opponents of 3 and 4, is also relevant. If either of these differences (1 minus 2, or 3 minus 4) is 200 points or less, then the transposition was in order, since in round 2 color equalization (rather than color alternation) was the issue.

But you figured out all of that, in your very next sentence. :slight_smile:

Incidentally, I originally made a huge error (momentary brain lapse) in my previous post, so please read it again (the edited version). It “crossed in the mail” with your reply.

Also, I forgot to answer your other question, namely, what the colors would be if the transposition is NOT made. The answer: When two players are paired against each other who have identical color history, the higher-ranked gets due color. “Higher-ranked” means higher-scoring. If the two players have the same score, “higher-ranked” means higher-rated. In this case, you are higher-ranked (higher-scoring), so you would get your due color (black).

Bill Smythe

7

Thanks for the explanations. I suspect I’ll have black against player 2 next round, then, since the rating difference between 2 and 3 is almost 300 points, so they’re unlikely to transpose just to keep colors alternating.

–Fromper

8

Right, and that’s just as well, because of the small-tournament effect. Because of this, if I were the TD, I wouldn’t transpose even if the rating difference were only 1 point. With only 8 players, you want some bad colors in round 3, otherwise you’ll get them in round 4, which is far worse.

Bill Smythe