Pairing System: Accelerated Pairings

Accelerated pairings alter the basic rules of Swiss System pairing in the early rounds in an attempt to reduce quickly the number of perfect scores. Through the Pair As box on the Add/Edit a Section dialog box, you can request accelerated pairings for a section, using any of three possible systems: Standard Accelerated, 1/6's Accelerated, and All Rounds Accelerated. Standard Accelerated is the only option in the FIDE Rule Set.

Standard Accelerated (USCF/General Rule Set)

If you choose the Standard Accelerated method in the US Chess/General Rule Set, WinTD does the following:

Round 1:

Players are divided into four (roughly equally-sized) groups from highest ranking to lowest. Call them A1,A2,B1 and B2 from top to bottom. Group A1 plays A2, B1 plays B2. With normal pairings, A1 would be playing B1 and A2 would be playing B2. Thus the stronger players (in A1 and A2) will have tougher competition in the first round under accelerated pairings, the weaker players (B1 and B2) will have easier games. In effect, the first round pairings are more like typical second round pairings.

Round 2:

Winners from A1 versus A2 play each other. Non-winners from A1 versus A2 play winners from B1 versus B2. Non-winners from B1 versus B2 are paired normally.

Accelerated pairings work to reduce the number of perfect scores faster than normal pairings if the non-winners from A1-A2 win most of their games against the B1-B2 winners. If the B1-B2 winners take a fairly high percentage of games off the A1-A2 non-winners, accelerated pairings will produce more perfect scores, not fewer.

US Chess recommends using accelerated pairings (only) if both of these are true:

1.the number of participants is more than 2 to the power of (number of rounds plus one).

2.there is a large difference in playing ability between the strongest and the weaker players. They make little sense where the difference between the top and bottom half is only 100 rating points or less.

We would recommend one additional requirement: that the ratings of the players fairly represent their skill level. It is much more likely that they will fail to reduce the number of perfect scores if there is a high percentage of unrated or provisionally rated players.

This implementation of accelerated pairings is similar to US Chess Variation 28R2. WinTD can also do the somewhat simpler 28R1 (added score) method, which pairs the top half players in rounds one and two as if they have a point added to their score. These differ in the second round handling of A1-A2 draws. WinTD's default method pairs them against B1-B2 winners—under the added score method, they play each other. The WinTD method is better for reducing the number of perfect scores. If you want the added score method, check the Added Score Accelerators box in the Pairing Rules tab in the Add/Edit a Section dialog box.

WinTD's version of accelerated pairings differs from that in the US Chess rule book in two respects: 1) the player's ratings aren't adjusted and 2) the bottom half non-winners are paired normally, rather than being pooled.

WinTD chooses the break point between the A's and B's by rounding up to an even number of players in A. For instance, with 66 players, WinTD will put 34 in A and 32 in B. If you want a different break point, you can check the Input Accelerate Break box on the Pairing Rules tab in the Add/Edit a Section dialog box. With this on, you will be prompted for the break point when a round is paired. (The Accelerator Break dialog box pops up after the Pair a Round dialog box).

Standard Accelerated (FIDE Rule Set)

Under the FIDE Rule Set, the standard acceleration method is the Baku system. This changes the points (for pairings purposes only) of the top half of players (rounded up to an even number) across the first half (rounded up) of the rounds in the tournament. It adds a full point for the first half of the accelerated rounds (again, rounded up) and a half point for the remaining accelerated rounds. For instance, if you have 121 players, 9 round tournament, the top "half" of players is 62. With 9 rounds, the first 5 are accelerated, and the first 3 of those are the full point accelerated while 4 and 5 are half point accelerated.

1/6's Accelerated (USCF/General Rule Set only)

The 1/6's Accelerated choice is similar to US Chess Variation 28R3. This divides players into sixths, and has the top sixth play the second, the third play the fourth and fifth play the sixth. In the second round, the winners from the games between the top two sixths play each other, while the other winners (from the lower groups) are paired against the non-winners from the high groups. This has not been used much. Because roughly two thirds of first round winners are paired against higher rated non-winners in round two, it has the potential to reduce the number of perfect scores faster than standard accelerated pairings, but is likely to do so only if there are a fair number of draws in those second round matchups. (The rating gaps are smaller in 1/6's accelerated, so if most games end decisively, the lower rated players will win a higher percentage than with standard accelerated pairings).

All Rounds Accelerated (USCF/General Rule Set only)

The final choice in this is to "accelerate" All Rounds. This never should be used in a real tournament. It distorts the pairings all the way through the tournament, giving the stronger players tougher games and the weaker players easier games. Use this only for warm-up tournaments where your goal is to give appropriate competition to everyone, and scores and prizes are of little concern. This is implemented using the added score method throughout; that is, a player in the top half will be paired as if he has an extra point. The 1-2, 3-4 pairing method is also good for this purpose.