The important features were: the number of appositions (features 7, 8) and relative clauses (feature 9), number of mentions within the document set (features 0,1), total number of apposition, relative clauses and copula (feature 12), number of high frequency pre-modifiers (feature 18), and the minimum bigram probability (feature 17).
the lexical and syntactic features were more useful than frequency features for determining familiarity.