Reader's Questions: Severity Scales
http://www.stcsig.org/usability/newsletter/9904-severity-scale.html

Wilson, Chauncey E.
Usability Interface
1999

Abstract:

It is important for the Usability Engineer to attend meetings where development and product managers review bugs, decide if the severity is appropriate, and choose which bugs will be fixed. I've been able to convince development and product management to consider some usability bugs as critical bugs.