Methinks that preexisting bias can exist so easily with online personality type testing - reading about the basic premise can affect one's scoring to a certain extent, even if an attempt is made to be impartial.  I was a member at one of the major Meyers-Briggs forums for a few years, and there was such pride attached to categorizing oneself as a certain type, as if this wasn't supposed to be an objective assessment of personality and were instead cliques to join.  It oftentimes seemed as if people gravitated toward the type they [i]wished [/i]they were.

I agree about similar temperaments attracting one another, to a certain extent.