Pete, I would normally agree with you, but we need to be careful to specify avoid negative stems in SUMMATIVE assessments. There is actually some good psych of learning literature that shows for FORMATIVE assessments, when they are still learning the material and using the quiz to practice, it may be BETTER to use negative stems because as they read the possible answers, they are saying to themselves "yes, that IS correct about xyz," more times than not, as opposed to positive stem, single correct answer questions, where they are forced to say "No, that is NOT true for xyz." It all depends on how important you feel it is to be able to describe characteristics that ARE part of whatever, or is it more important to know characteristics that are NOT true of whatever....