Arrow switching - BridgeBase Online vs F2F
One of the clubs where I play online in BBO runs their pairs evening as an arrow-switched Mitchell and declares a single winner at the end of the tournament. I've been thinking about this and I wanted to check how arrow-switching works in BBO.
Forgive me for stating what will be obvious to most of you, but I wanted to make sure I explain my thinking, not least so any missteps can be spotted ;-)
In a face-to-face pairs session, the boards move in one direction and the EW pairs in the other at the end of each round. When the TD makes the arrow switch, NS pairs will play a number of hands previously held by EW and vice versa. As long as enough boards are played like this, the results are sufficiently statistically significant to judge how EW and NS pairs fared against each other as well as against those pairs sitting in the same orientation. My understanding is approximately one board in eight need to be arrow-switched.
I believe the key point here is that each pair will play ~12.5% of the session's hands that were played by pairs in the opposite orientation and the remainder that were played by pairs in the same orientation.
My experience in BBO is that in each round, all tables play the same boards. This is certainly the case in the club where I play that uses an arrow-switched Mitchell. The question is how the arrow switch is implemented in BBO. If all pairs switch, then I will play hands that were played by pairs in the same orientation as me so the objective of a face-to-face arrow switch would not be satisfied.
So, the question...
How does an arrow switch in BBO work? What have I missed?
Thanks in anticipation.
Chris Woodhouse
Comments
The big difference between BBO and f2f in this regard is that BBO is barometer - everyone plays the same boards in each round.
Playing f2f, with boards sets moving up tables, we achieve an arrow-switch by switching NS/EW on one or two rounds at all tables, at the end of the session. 2 rounds out of 12 or more (2-board rounds), 1 round of of fewer rounds (3+-board rounds).
To achieve this with a mitchell movement on BBO would require switching NS/EW at one in eight tables on each round (different tables in different rounds). This is not something the platform offers.
BBO's set of movements is very limited. If you want a single-winner round-robin-style movement, your only real option is to play what BBO calls a "Howell" (but it isn't an actual Howell and is probably a lot more unbalanced than the real thing).
It would certainly be possible in theory for a bridge platform to implement arrow-switching by switching some players but not others each round (working out the optimal pattern for this might be quite interesting); obviously, when playing barometer, you can't just arrow-switch particular rounds because that doesn't help at all. However, BBO doesn't currently implement anything like that.
Thanks, @Robin_BarkerTD and @ais523