A study conducted on performance review ratings using pen and paper versus email found that peers negative appraisals were more via email than when giving reviews in writing.
In a diary study by Jeff Hancock, participants confessed to being dishonest mostly on the phone and least in an email. Face to face and instant messaging results were of an equal conclusion and positioned in the middle of the other means.

Weinschenk, S., PH.D. (2011). 100 Things Every Designer Needs to Know About People [Kindle]. pg. 154