The limitations of grapevine

We all rely on informal information exchanges; I have written about it before. Here is another story that shows what are the strengths and the limitations of the grapevine as an information channel. In Spring, I have received several informal reports about one of our adjunct faculty having problems in interaction with students, with work ethic, and perhaps with competence. We are not obligated to provide work to any part-timers, and actually have a large reserve pool. My plan was to check on the rumors, and if they prove to be correct, look for someone else to hire.
We have collected student feedback from a series of surveys, so there was actually some data to verify the story. What I discovered is that just one unhappy student was the source of all the reports I received. Imagine how it works: this one student has several classes, and voices the same concern with several instructors. She may pose it in a way that implies other students were also treated badly. The instructors all tell me that there is something I should know about. Of course, they don't mention the student's name, because of confidentiality of the initial conversation, and because the source may have strengthen her case by implying it is a larger problem. Because the story changes with each transmission, soon it sounds like three different stories. Moreover, faculty talk among each other, and a person who have heard it from another faculty, tells me about the problem in yet another form. Considering that I actually receive an astonishingly small number of complaints, three or four comments about the same person sound like a lot.
From the students' comments, it transpires that we perhaps did not provide clear enough instructions and expectations to this new part time faculty. Not only am I no longer sure if there is a personnel problem in the first place; it may have been our program's problem. I am now thinking it may have been only a small personnel problem, which is easier and fairer to solve by providing a little more training and support to the instructor, rather than rushing to replace her or him with someone else. The new person may have other problems, after all. And who does not?
The grapevine is a great way to alert about a possible problem. It is not really good at determining cause or the extent of the problem, nor is it a good helper in making any decision. This blog is more of a note to self, because I don't want to discourage people from sharing what they know with me or with each other. This is how we improve, and develop our professional community.