The two-step flow of communication model hypothesizes that ideas flow from mass media to opinion leaders, and from them to a wider population. It was first introduced by sociologist Paul Lazarsfeld "et al." in 1944 and elaborated by Elihu Katz and Lazarsfeld in 1955 and subsequent publications. Melvin DeFleur and Sheoron Lowery argue the book was much more than a simple research report: it was an effort to interpret the authors' research within a framework of conceptual schemes, theoretical issues, and research findings drawn broadly from the scientific study of small groups Unlike the hypodermic needle model, which considers mass media effects to be direct, the two-step flow model stresses human agency.