Anybody who wants to discuss the always fascinating--and sometimes contentious--topics of appropriate authorship of scientific publications, head on over to Blue Lab Coats and join the conversation about these scenarios:
Let's say that you have 3 employees- doesn't matter if they are students, postdocs, techs or whatever, working on a single project, basically using the same technique to get at the same question. (And we almost certainly discuss whether this is a great strategy for giving people projects to begin with, and for the record I don't do this in my lab...but that is not the question right now.) Scientist A and Scientist B do lots of experiments, but the data is never great enough to appear in print. Scientist C has awesome hands, and gets the thing to work- and work beyond your wildest imagination. Do you include all of them on the paper that eventually makes its way out of the lab on this work, or not? Does it matter if they are in the lab concurrently or not?
Now let's imagine that Scientist B, despite the fact that his/her experiments were a total bust, was letting Scientist C look over his/her notebook- and they were spending a lot of time troubleshooting together over beers on Friday afternoon-.... does that change your opinion of who should be on the paper...?
We are going to build on scenario #1 up there for this. For your own lab members you decide - in the case where Scientist C was wildly successful without input from Scientist B (i.e. both A and B performed failed experiments)- you decide that only Scientist C should be on the paper. But you've got a collaborator who has to make similar sorts of decisions to determine who will be authors on a collaborative paper... from both of your labs. Your collaborator has the philosophy that the lab is a team, and that no matter whether or not particular individuals produced actual data that appears in the paper....
I think you see where I am going here- how do you reconcile who goes on the paper from each lab. Does each PI decide independently who from their labs should be included, or do the PIs have to have some sort of agreement about what constitutes enough of a contribution to be included as an author?