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The out-group comparison method of character analysis. Syst. Zool., 30:1–11.—An operational rule for analyzing character polarity with out-group comparison is presented and a series of observations, including potential problems in applying the rule, are discussed. The “commonality principle” (=“frequency of occurrence,” “common equals primitive”) for determining character polarity is reviewed and dismissed as a reliable alternative to out-group comparison. Based on the rule and observations, a general method for character analysis is synthesized.
Watrous et al. (Sun,) studied this question.