[AL78]

My local bridge club is re-introducing a F2F evening session, and the decision at the committee meeting was to keep the online session in parallel, play the same boards in the two sessions, and merge the two sessions into one when scoring so the final result is as if there was only one session. My question is, is this likely to introduce any bias in the results, given that if there were two Mitchell movements for example, half the EW pairs will not play half the NS pairs, and if there is a difference in strength between the club and online sessions, some players will play against a greater proportion of stronger players which will make it harder to do well?

I know that in a big EBU event like the Brighton congress this effectively happens (it is impossible for everyone to directly play everyone sitting the other way), but I expect in that situation the mean and variance of the standard of the subset of the direct opposition anyone plays against at their table is going to be very similar.

[pescetom]

I think the obvious answer is yes, there will be bias induced by differences in strength between the sections and (probably) by the small size of at least one of the two. It still sounds like a fun and sensible way to proceed, avoiding polarization into two opposing factions. Everyone recognises that club tournaments are a bit randomic anyway and what really matters is to be able to say "we were the only ones to make the slam" at the bar later