Michael J. Mauboussin authors this white paper (PDF) on 'investment comparisons.'

The facts are these: (a) value is determined by the comparison of one thing with another; (b) there is more than one kind of comparison we can make in any given instance; and (c) we may value something more highly when we make one kind of comparison than when we make a different kind of comparison.
Daniel Gilbert
Stumbling on Happiness