May 21st 2012, 17:31 by W.W. | IOWA CITY IN a recent post on the constitutionality of the filibuster, I floated the opinion "that polarisation is due mainly to increasingly efficient sorting of American voters into parties according to personality type", without offering any evidence or explanation, as several commenters were right to observe. I'm happy to admit that this is an idiosyncratic hypothesis, and that I therefore owe readers at least a sketch of the reasoning behind it.First, conservatives and liberals do tend to differ in terms of personality. This is a well-known, well-confirmed proposition in political psychology. Among the "big five" personality traits, two are significantly associated with ideological sympathies. "Conscientiousness" is pretty much what it sounds like. Wikipedia helpfully notes that, "Recently, ... Continue reading →