The continuity of descent amongst the various branches of the original, middle Byzantine family is not clear, and historians generally recognize several distinct groups of Doukai based on their occurrence in the contemporary sources. According to Demetrios I. Polemis, who compiled the only overview work on the bearers of the Doukas name, in view of this lack of genealogical continuity "it would be a mistake to view the groups of people designated by the "cognomen" of Doukas as forming one large family".