Since McAdam published his book outlining the theory, revisions to it have been made by him and other sociologists, so today it differs from McAdam's original articulation. As sociologist Neal Caren describes in his entry on the theory in the Blackwell Encyclopedia of Sociology, political process theory outlines five key components that determine the success or failure of a social movement: political opportunities, mobilizing structures, framing processes, protest cycles, and contentious repertoires.