empath is a similarity analysis of the 63,000+ heavy-metal bands listed in the Encyclopaedia Metallum (as of 30 October 2008), based solely on overlap of positive reviewers. Each pair of bands is scored, approximately, on the percentage of positive reviewers in common (positive = average rating 50% or higher). The overlap must be at least 2, and the scores are weighted to reduce the effects of both high popularity and small samples. The lists are cut off at 30 or a minimum score of 0.03, whichever comes first. 2177 bands qualify. The bigger the band's name in the index, the more similarities it has.
 
All displayed precision is for entertainment only; no statistical significance is asserted. Aesthetic judgments are probably implied, but not mine.