Citing personal communication for preliminary results I am writing a paper with a group of people, and we would like to cite preliminary results from another work, which one of the coauthors is involved along with yet other people. The preliminary results have not been published or even written up. Should we cite this as "Personal communication" and put the names of all members of the other group (which overlaps with the current group), or are there better ways to do it?
I hate to disappoint you, but you would be referencing the material which is impossible to get. The reviewers do see it similary and complain, and they are right in doing so. Personally, if there is any way whatsoever to convince the other group to write up the preliminary results and put them on a web page in time, do it. See point 7 in most harmful heristic. Probably, the best you could do now is saying &quot;to be published in [SB]&quot; where the reference is a half-hearted entry along the following lines:

[SB] John Smith and Joe Blotz, The Importance of Being Published, 2017, in preparation.

Adapt the title, of course.