Duplicate bridge movements

A duplicate bridge movement is a scheme used in a duplicate bridge tournament to arrange which competitors play which opponents when, and which boards they play. The arrangement has to satisfy a number of constraints which often conflict to some extent, and compromises may be required. The resolution of these compromises is to a considerable extent a matter of taste, and if possible the players should be consulted as to their preferences.

Movements are categorized by the type of event—Individual, Pairs, or Teams.

The requirements for the movement are as follows:

It is important that once the movement is selected, it should be completed: uncompleted movements are likely to be unbalanced. Thus a movement should be selected which has a high probability of being completed.

In two-winner movements, the NS pairs play the EW pairs, but never other NS pairs. There are thus two "fields" competing separately. If the average standard of the NS and EW pairs is different, this can give an unfair result.

In one-winner movements at certain points NS pairs play as EW and EW pairs play as NS, e.g. through an arrow switch (reversing the polarity of tables during some rounds). This creates a one-winner movement.

The number of rounds which are arrow switched affects the fairness of the result. Normally between one-eighth and one-quarter of the rounds are arrow switched. The English Bridge Union (EBU) recommends one eighth. So in a 7 or 8 round movement, you would arrow switch the last round.

There are two basic types of pair movements—Mitchell and Howell. Mitchell movements can be two-winner or one-winner. Howell and variants of Mitchell are one-winner.

In a standard Mitchell movement (also known as "straight Mitchell"), there are two separate groups of players—one group always sits North-South, and the other always sits East-West. North-South players remain at the same table throughout all rounds of play. After each round, boards move to the next lower numbered table (from table 1, boards go to the highest numbered table), and East-West pairs move to the next higher number table (at the highest numbered table, pairs move to table 1). Pairs are typically identified by the direction they are sitting, coupled with the table number they start at.

This arrangement can be followed without modification when there is an odd number of tables, with no additional pairs left over (no half-tables). Modifications to the straight Mitchell movement must be made whenever there is an even number of tables, or a half-table.

A straight Mitchell movement requires that the number of rounds played R is equal to or less than the number of tables T. Hence, if there are 8 tables and time to play 24 boards, a maximum of 8 rounds can be played and there will be 3 boards per round.

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