Here’s a presentation by Dan Ariely a professor of behavioral economics at Duke University (website). He’s author of the book Predictably Irrational: The Hidden Forces That Shape Our Decisions (2008). His speech here is a little difficult to understand, but it’s worth the effort.
The most interesting aspect I took from the presentation was the part about Asymmetric dominance (starting at 12:20). Briefly put, if you have two primary choices (“A” and “B” below), but add a similar, yet inferior alternative to one of them (“C”), it makes people more likely to pick the choice that is superior to the inferior alternative (B), even though it’s no better than the other primary choice (A). In other words, the existence of a bad (C) tilts peoples’ perception in favor of (B).
A<------------>B<-->C
So, Ariely concludes, if you go out bar hopping, you want to take along a slightly uglier friend.