Provide the information needed but do it with positive remarks.  Avoid negative statements and anything that would be embarrassing if quoted in public.  Example:

> 1. Prof. X has an ambitious research program.  This group attracts students who come in with extensive prior research experience.
>
> 2. Prof. Y is much sought after as an invited speaker.  Due to his/her conference travel commitments, s/he tends to attract students with a high degree of self-sufficiency.
>
> 3. Prof. Z is a relatively recent arrival in the department.  S/he provides a solid training in lab techniques and a strong suit is guiding students in defining their research question.