Thread: Accelerated vs Abominated Swiss Pairings :)

1. Accelerated vs Abominated Swiss Pairings :)

A common form of accelerated Swiss pairing tournament seen in Australia goes like this:

1. Put the top half of players in one group and the rest in another.
2. Add one notional point to the top half for the purposes of doing the draw for the first two rounds only. Thus the top-halfers are paired as if they are on 1/0, and a top-halfer is paired as if on 2, 1.5 or 1 out of 1 for round 2 depending on whether they won, drew or lost round 1.
3. Remove the notional point after round 2, so that for round 3 those who have had two wins are in the same scoregroup, no matter who they defeated or where they came from in the draw.

This system is known to Wikipedia as "Accelerated Pairings" because Wikipedia's chess sections are for the most part written by Americans. The correct name of this system (and its variants) shall henceforth be Abominated Pairings and any event in which it occurs shall be an Abominated Swiss, especially if it is directed by an IA, since one would hope IAs would know much better.

A much better system of Accelerated Pairings that has been used in the UK (although I am unsure what the current situation is with the BCF acceleration rules) is discussed in Reuben's books (at least the first edition thereof). In comparison to Abominated Pairings:

1. The first round is effectively the same (top quarter vs second quarter, third quarter vs fourth quarter).

2. There is no notional added point. Instead, those bottom half players who are on perfect scores after a given round are paired against top half players who are not on perfect scores (listed in rating order irrespective of score provided they have not dropped >1 point), while top half players on perfect scores play each other. This is the only form of acceleration that exists (although for very long tournaments it is possible to apply similar principles to scoregroups just below 100% too) .

3. There is no fixed number of rounds after which the acceleration in step two is removed. Instead, it is removed once there are no bottom-half players left on a perfect score. Sometimes this is the case after round two, more often after round three, in rare cases it may take until round four to do the job. However, once the number of bottom-halfers on a perfect score is small, the difference between the draw and a normal Swiss draw for that round is not great, as only a few pairings are affected.

4. Just in case some upstart from the bottom half (perhaps an unrated or inaccurately rated player) keeps winning and winning and winning, the acceleration is never applied to the last two rounds.

To consider which of the systems does the job better we need to consider the objectives of acceleration. The first objective of acceleration (and the reason such systems were invented) is to cull the perfect score group as quickly as possible and thus increase the chance of an event with many players but few rounds having an outright winner rather than co-winners each on perfect scores. The second objective is to eliminate the vast mismatches seen especially in round 1 of a normal Swiss.

The Abominated Swiss is much less effective than the Accelerated Swiss at culling the 100% scoregroup, for two reasons:

Firstly, in the Abominated Swiss the bottom half winners in round 1 are then paired only against the top-half losers (and, if insufficient top-half losers, with each other, which is an even bigger problem). But allowing them to also be paired against the top-half players on 0.5 means that the bottom-half winners play a stronger list of players and therefore fewer of them are likely to make it to 2/2.

Secondly and more importantly, when the Abominated Swiss removes the acceleration after round 2, opportunities to cull the bottom-half 2/2s by feeding them to top-half 1.5/2s and 1/2s are lost. For instance, in one such event I looked at tonight, the acceleration was removed after round 2 with 14 players on 2/2 of which 5 were from the bottom half. After this round there were still five players on 3 (and it would have been 6 but one of the bottom-halfers very surprisingly drew across a c. 900 point mismatch). Under a proper accelerated system, the five bottom-halfers on 2/2 would be fed to the top end of the top-halfers on 1.5 and 1, most likely none of them winning. The remaining 2/2s could play each other (except for one floating down) and most likely the top score group would be culled to 2 or 3 players.

That said, all five leaders were removed from the 100% scoregroup in round 4 anyway, which just goes to show why acceleration to cull the lead group is frequently unnecessary anyway. There are widespread delusions that if your number of rounds is n and you have more than 2^n players then you need acceleration to get the 100% scoregroup culled by the event's end. In fact, there are often draws on the top boards.

Also the inadequate culling of the 2/2 scoregroup in the Abominated Swiss produces grotesquely unfair discrepancies in opponent strength, with some of the round 3 100%-group pairings very competitive games and others effective one-point byes.

As for the avoidance of mismatches, the Abominated Swiss does give much closer round 2 pairings among the .5/1 top-halfers, and also slightly closer round 2 pairings in the notional 1/1 scoregroup (top half losers vs bottom-half winners mostly). But because it is less efficient at culling the 100% scoregroup, it often leads to some massive mismatches on top boards in round 3 (c. 1000 points not at all uncommon) so the gain in mismatch avoidance compared to true acceleration is questionable.

It can also be argued that pairing a top-halfer who drew in round 1 with another in the same boat is perverse. The second-quarter player who drew in round 1 with a top-quarter player is paired with another top-quarter player. This is a tough round 2 pairing for both and it will most likely result in either: (i) the second-quarter player going to 0.5/2 while other second-quarter players who lost round 1 have easy wins and go to 1/2 or (ii) the top-quarter player drawing again and now being 1/2, and most likely getting a very big mismatch in round 3.

So why is the Abominated Swiss so common? Because it's a solution to a problem that is simple, elegant and wrong. Computer programmers who are not familiar with the intricacies of pairings debates (there being no specified FIDE acceleration system) find it easy to write programming modules that just add a point to the score then take it off after a certain number of rounds. SP offers only this as an acceleration pairing option, and I am not sure if any other program offers anything but this "bonus point" system.

It is worth noting, however, that in SP it is possible to change the round at which the accelerated pairings are removed through the tournament, and thus to run a hybrid Accelerated/Abominated system in which you continue the bonus point until the 100% scoregroup contains only top-half players. This is extremely easy to do, eliminates a lot of round 3 hassles with Abominated pairings, and it is therefore surprising that it is not done more often.

I realise that true acceleration is somewhat impractical if you have to do it by hand. But if those using SP-acceleration would at least keep the acceleration on in round 3 if there are still bottom half players on 2/2 then that would be significant progress.

This can be done in SP as follows: In Options: Tournament: Accelerated Pairings initially set "Stop acceleration AFTER round" to 2.

The instant a bottom-halfer on 1/1 wins round 2, change the 2 to a 3.

Is that too difficult?

2. Well-argued case

A very well-argued case, Kevin. I agree with you. The current accelerated system you described is indeed an abomination. The second system sounds much better.

3. Yes, and it sounds easy to implement, even with SP. If I ever get into that situation (so long as the players know in advance what acceleration will mean, as to opposed to abomination) and it is deemed appropriate that it be done (not that this is a foregone conclusion by any means), then it would be interesting to put it into practice, and to get feedback on it.

4. I am opposed to the first form of accelerated pairings.

I have been in a tournament when a 1400 player was leading with 4/4
while Ian Rogers only had 3.5/4. its essentially a handicap system. All sorts of silly things happen.

Neil Davis once made the point that if you get a notional point you should
get to keep it at the end of the tourney.

Haven't read through the second type yet.

A very well-argued case, Kevin. I agree with you. The current accelerated system you described is indeed an abomination. The second system sounds much better.
Hear Hear

I also think that acceleration is often used when it is not needed and in those circumstances can actually increase the possibility of ties for first place.

6. Originally Posted by FM_Bill
I am opposed to the first form of accelerated pairings.

I have been in a tournament when a 1400 player was leading with 4/4
while Ian Rogers only had 3.5/4. its essentially a handicap system. All sorts of silly things happen.

Neil Davis once made the point that if you get a notional point you should
get to keep it at the end of the tourney.

Haven't read through the second type yet.
I'm running a low level unofficial tournament at an elementary school and am sorting through all the nuances and variations in pairing theory. The kids range from barely knowing the rules of play to about 520 ELO. In order to have a more enjoyable experience for all, I tried to avoid the unpleasant extreme pairing mismatches and decided to use accelerated pairings. It seems most logical to not remove the acceleration point in this setting. Do you have any more information about what Neil Davis said about it and whether anyone uses this method?

7. Originally Posted by Danko
It seems most logical to not remove the acceleration point in this setting.
The main risk there is that if someone who you seed in the bottom half is actually very good and just keeps on winning, they could reach a perfect final score without playing the tournament leaders. That is why it is normal to at worst remove the acceleration two rounds from the end. However if you have lots of rounds for the number of players then that situation gets sorted out.

8. Originally Posted by Kevin Bonham
... they could reach a perfect final score without playing the tournament leaders.
But that's why it seems that keeping the point would be necessary, since even with an undefeated record, a player from the lower half would still be a point lower than a person with a perfect record from the upper half. I think that seems fair. A player from the lower half could still come in first, but it would require doing a point better than someone facing tougher competition in the upper half.

However, after having applied this idea to a school tournament that has now been through 4 rounds, I do have the uncomfortable situation of having to try to explain to the kids the logic behind giving the strongest players a bonus point. If we hadn't done the acceleration at all, the first round would have been such huge mismatches in our club that it would have been a waste of time to even play it. Even though we applied it to the first round, the mismatches were big enough (since there is such a wide range of ability in our club) that the results came out predictably with only one exception at the very bottom level. If acceleration were removed after round one, it turned out that the matchups were just about exactly the same blowout pairings as if we were playing that unaccelerated first round that I thought we had avoided. And so the acceleration bonus point was kept. Beyond that round, removing the point didn't seem fair to the players that had had to face tougher competition for the first two rounds compared with those that had an easier time in the lower half. But perhaps this was my mistake as a first time tournament organizer.

Since this was just an unofficial school tournament it gave room for some tinkering to try to make it a better experience for the kids, without hugely mismatched games and postponing the climactic pairing of the top two til the final round. Unfortunately it has been much harder than I expected and there doesn't seem to be a perfect solution to achieve the ideals without the downsides. Maybe avoiding a Swiss System would be better next time and going with an imperfect but easier to understand single elimination system.

9. Originally Posted by Danko
But that's why it seems that keeping the point would be necessary, since even with an undefeated record, a player from the lower half would still be a point lower than a person with a perfect record from the upper half. I think that seems fair. A player from the lower half could still come in first, but it would require doing a point better than someone facing tougher competition in the upper half.
Yes - and that might be out of their hands, because they can't control it if a top-half player keeps winning and never plays them. Then the bottom-half player might complain that they had been denied their shot at the tournament win through no fault of their own just because their rating was poor. Admittedly, it is a pretty unusual scenario, since typically either the top half will sort themselves out, or any overperforming bottom-halfer will get sorted out somewhere.

However, after having applied this idea to a school tournament that has now been through 4 rounds, I do have the uncomfortable situation of having to try to explain to the kids the logic behind giving the strongest players a bonus point.
I sympathise with this because sometimes I've found that even very good ideas are a hard sell to children if there is anything about those ideas that smacks of potential subjectivity or special treatment. It's good that so many children have "got" the concept of fairness on such a basic level but they don't have the experience base to understand about cases where there can be good reasons for treating different skill levels differently.

If acceleration were removed after round one, it turned out that the matchups were just about exactly the same blowout pairings as if we were playing that unaccelerated first round that I thought we had avoided.
Yes. Under normal circumstances removing acceleration after round one is almost totally pointless since it just switches rounds 1 and 2. Acceleration only does things if you keep it on for at least two rounds.

Beyond that round, removing the point didn't seem fair to the players that had had to face tougher competition for the first two rounds compared with those that had an easier time in the lower half.
This is one of the negatives of an accelerated system - in the early rounds score and performance don't have much to do with each other in the middle of the pack. Typically a player from the second 1/8th of the field will play a player from the fourth 1/8th and a player from the first 1/8th, scoring 1/2. A player from the seventh 1/8th of the field will play a player from the fifth 1/8th and a player from the eighth 1/8th, also scoring 1/2. Thus the differences in strength of field met in the first two rounds in the same scoregroup are much greater than in a single swiss.

However, there is some compensation, because when the acceleration is taken off those who've had a hard run to a midfield score should get a very easy opponent while those who have had an easy run should get a hard opponent.

Unfortunately it has been much harder than I expected and there doesn't seem to be a perfect solution to achieve the ideals without the downsides. Maybe avoiding a Swiss System would be better next time and going with an imperfect but easier to understand single elimination system.
Divisions are one alternative but then you have to explain how some players are in one division and some in another. Eliminations have the disadvantage that not everybody plays all games.

Some of these problems don't have perfect solutions and everything you do has disadvantages of some kind. Are the stronger players typically much older in your case or is it an even-age group?

10. Originally Posted by Kevin Bonham
Are the stronger players typically much older in your case or is it an even-age group?

Now that we are through the fourth round with a couple surprises, there is a chance we will have a three way tie for first place after the final round. So now I have to consider the tiebreak options. In the event of a tie, I hope we can just call them all co-champions and make them all happy, but I'm afraid the school will probably want a single winner to place on a plaque. If we have to have one single winner, I'm inclined to have a round robin playoff between the last three, rather than leaving it up to tiebreak points which seem to leave too much to luck.

11. Originally Posted by Danko
If we have to have one single winner, I'm inclined to have a round robin playoff between the last three, rather than leaving it up to tiebreak points which seem to leave too much to luck.
And which leave someone feeling left out too. In the Aus Juniors when there is a more than two way tie, tiebreaks are often used to cut the tied players to two, then they play a match, but at inexperienced junior level it is much harder for players to understand that sort of thing.

12. Been looking further at accelerated pairings for the tournament this weekend.

Something I have picked up which is a concern is to do with floats. With those bottom halfers on 1/1 being fed to top halfers on less than 100% in round two, this increases all the number of players who will have upfloated or downfloated in round two, meaning that for round three, it will be harder to make decent pairings.

This could be even worse in round 4 if the acceleration is removed after round three because almost all players will have a strong colour preference ie plus 1 or minus 1.

This could mean an arbiter needs to go quite a way down a score group to find a pairing that meets the dutch pairing rules.

Perhaps in acceleration tournaments, the floating rules should be ignored

13. Originally Posted by Garvinator
Perhaps in acceleration tournaments, the floating rules should be ignored
Yes, for an Acclerated Swiss, a score difference that is forced by the acceleration should not be regarded as a float. (There may still be some floats that are not forced by the acceleration.) However, I'm not sure how computer programs that employ "acceleration" go with this. Even if you do accelerated pairings manually and then go back to computer pairings once the acceleration is taken off, it may still regard point-mismatches from previous rounds as floats. To avoid this it may be necessary to pair the whole accelerated tournament by hand, which is OK if you have only one round a day but a bit of a pain otherwise.

I have just tested SP's "acceleration" and found that it classifies a top halfer on zero playing a bottom halfer on one in round 2 as a float. This is incorrect.

14. I think the issue of identifying if a person is a genuine floater or an accelerated floater could be one of the main issues for pairing programs in doing accelerated pairings.

In round two there are couple of 0.5 v 0 pairings, where the 0.5's drew against each other in round one (top half pairing).

So in my opinion the two 0.5 ers are downfloaters as they playing someone on 0 who are also top halfers.

Probably the best way to describe what to do is:

1) While acceleration is being applied or is a factor, if two players are playing each other and they are from opposite half of the draw, then floats are not applied.
2) If they are from the same half of the draw, then float rules do apply.

15. I am not sure if it is even possible in any pairing program to manually change someone's float status. That would be a handy feature for acceleration.

Arbiter works who were the genuine floaters for a particular round, adjusts the float status of the required players and then pairs for next round.