The two-step flow of communication

This model by Lazarsfeld and Katz hypothesizes that ideas flow from mass media to opinion leaders, and from them to a wider population.
Personal influence came to illustrate the process intervening between the media's direct message and the audience's reaction to that message. For example, the James Bulgar case; a boy told his friend about a film he had watched and influenced the other's behaviour.
The two-step theory refined the ability to predict how media messages influence audience behaviour and explains why certain media campaigns do not alter audiences' attitudes.
However, the hypothesis has been critised by myriad consequent studies, saying they find substantial evidence that initial mass media information flows directly to people on the whole and is not relayed by opinion leaders.