Wikipedia 10K Redux by Reagle from Starling archive. Bugs abound!!!
It is not at all easy to say what an ''expert'' is. This is actually studied in EpistemOlogy under the general heading ''ExpertKnowledge''. On one account, put very roughly, an expert is a person who is (or, perhaps, is widely recognized to be) a reliable (see ReliabilIsm) source of KnowledgeByTestimony for other people.