BBO Mitchells

[SeanBothar]

In a previous post on BBO Swiss Pairs the question of switching in Mitchells was raised.

BBO Mitchells are different from ordinary Mitchells because all the same boards are played at each table for each round.

So for a 13T 13R 26B Mitchell on BBO boards 1 & 2 are played at all tables in round 1, boards 3 & 4 at all tables in round 2 and so on.

For a 13T 13R 26B Mitchell in club "live" competitions switching is normally done on rounds 12 & 13 to give a one winner result.

Many may not be aware that if the same switching was applied on R12 & R13 to a BBO 13T 13R 26B Mitchell this would have no impact at all on the balance.

To understand this consider the "travelling" scoresheets for a 13T 13R 26B Mitchell switched on rounds 12 & 13.

For the "live" club Mitchell, two EW pairs (#14-#26) are in the "NS" column and two NS pairs (#1-#13) are in the "EW" column on each traveller. This is what gives the comparison between NS pairs and EW pairs and gives a fair one winner result.

Now look at boards 23 to 26 on the BBO Mitchell if switching was applied on R12 & R13.

All the EWs (#14-#26) are in the "NS" column and all the "NS" (#1-#13) are in the "EW" column so there is no comparison at all between the NS pairs and the EW pairs. That is why switching on R12 & R13 has no impact at all on the balance with BBO Mitchells.

If switching in needed on BBO Mitchells there has to be a different approach.

Staying with the BBO 13T 13R 26B Mitchell example, switch table 1 on rounds 12 & 13, table 2 on rounds 11 & 12, table 3 on rounds 10 & 11 and so on to table 11 on rounds 2 & 3. Table 12 is best on R13 only and Table 13 on round 2. This gives an excellent balance as good as the "live" club Mitchell.

Forum users will undoubtedly all agree that this is far too complex to code into the movement instructions so unswitched Mitchells have to remain the only option!

[Vampyr]

This is very interesting; I had never thought of this. Of course software. An do what could not reasonably be done live, which is arrow-switch different boards for different pairs. Even randomly allocated arrow-switches woul produce some semblance of a one-winner movement.

 

But at least clubs that run IMP pairs are prevented from arrow-switching, as trying to produce a one with a game in those competitions is just adding another randomiser into a game which is already a crap shoot.

 

Swiss pairs could use more balance, and arrow-switching would be nice (though not, as you point out, in a Barometer) but of course there is natural switching at least between rounds. as the higher-ranked pair at the table plays N/S and the other plays E/W.