> often see smaller groups as outliers

Is there a name for that phenomenon? I saw a similar thing in some data that we were looking at recently, and it took a while to work out that the reason why one group's number was consistently a bit smaller than another group's number was that we were simply taking the max of a smaller group. it's obvious in retrospect, but can catch you out if you're not expecting it.

I'd like to have a name for it, a reference to send people to.