Lazarsfeld's Two-Step Flow Theory of Mass Communication

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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[4] and elaborated by Elihu Katz and Lazarsfeld in 1955[5] and subsequent publications.[6] Lowery and DeFleur 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 [7] Unlike the hypodermic needle model, which considers mass media effects to be direct, the two-step flow model stresses human agency.

For example, in the field of science communication, Matthew Nisbet describes the use of opinion leaders as intermediaries between scientists and the public as a way to reach the public via trained individuals who are more closely engaged with their communities, such as

"teachers, business leaders, attorneys, policymakers, neighborhood leaders, students, and media professionals." Examples of initiatives that take this approach include Science & Engineering Ambassadors, sponsored by the National Academy of Sciences, and Science Booster Clubs, coordinated by the National Center for Science Education.[8]
^{According to Lazarsfeld and Katz, mass media information is channeled to the "masses" through opinion leadership. The people with most access to media, and having a more literate understanding of media content, explain and diffuse the content to others.
Based on the two-step flow hypothesis, the term "personal influence" came to illustrate the process intervening between the media's direct message and the audience's reaction to that message. Opinion leaders tend to be similar to those they influence—based on personality, interests, demographics, or socio-economic factors. These leaders tend to influence others to change their attitudes and behaviors. The two-step theory refined the ability to predict how media messages influence audience behavior and explains why certain media campaigns do not alter audiences' attitudes. This hypothesis provided a basis for the two-step flow theory of mass communication.[9]}