The media can and does have a strong effect on what people think about. By highlighting certain events repeatedly, they create a sense of urgency about those issues even though this is not always an accurate reflection of reality.
Reality is what is actually happening in the world pertaining to the economy, society, politics and science. The media selectively highlights certain events and gives them prominence. The criteria for the selection depends very much on the ideology of the media editors and their vested interests. By highlighting certain events an uncritical audience will perceive and construct the mediated reality as reality. One example is the royal wedding of Prince William to Kate Middleton, which mesmerised the world, including parts of the world that have no connection to the British monarchy. Discerning audiences may well ask why the wedding of two people, who are in no way related to them, is important enough to justify worldwide media attention, or indeed, how and why it might be relevant to them?
The agenda setting theory was formally developed by McCombs and Shaw (1972) when they studied the US Presidential Election of 1968. Their analysis of the news and media coverage found a strong correlation to the opinions held by the voters in Chapel Hill, North Carolina. Similar findings were found in the media study surrounding the murder trial of OJ Simpson (Salwen & Driscoll, 1997) and the attempted impeachment of US President Clinton (Yioutas & Segvic, 2003).
These videos explain the agenda setting theory in detail:
From calleno16 under Standard YouTube License
From CSIxxTwee under Standard YouTube License
From MEF via emjay23 under CC License
Obviously journalists cannot include everything that happens in the world on any given day in their Newspaper TV or internet news program.
Investigate a cross section of media sources on a given day – compare how and why the different sources choose, and then mediate, the events for their expected audience.
Then consider the question, are they accurately representing the importance of the issues of the day?
McCombs, M.E and Shaw, D.L. (1972) The agenda-setting function of mass media. Public Opinion Quarterly,36 (2).
Salwen, M. B., & Driscoll, P. D. (1997). Consequences of third‐person perception in support of press restrictions in the OJ Simpson trial. Journal of communication, 47(2), 60-78.
Yioutas, J., & Segvic, I. (2003). Revisiting the Clinton/Lewinsky scandal: The convergence of agenda setting and framing. Journalism & Mass Communication Quarterly, 80(3), 567-582.