During the 1940s, mass communication entrenched itself as a field in its own right. Lazarsfeld's interest in the persuasive elements of mass media became a topic of great importance during the Second World War and this resulted in increased attention, and funding, for communication research. By the 1950s, there were increased concerns about the power of the mass media, and with Elihu Katz, Lazarsfeld published "Personal Influence", which propounded the theory of a two-step flow of communication, opinion leadership, and of community as filters for the mass media. Along with Robert K. Merton, he popularized the idea of a narcotizing dysfunction of media, along with its functional roles in society.