EVALUTE THE CREDIBILITY OF THE FOLLOWING LIST OF SOURCES: NEWSPAPER, MAGZINE, TELEVISION PROGRAMS, MOVIES, TELEVISION NEWS REPORTING. THE INTERNET, AND ADVERTISING. WHAT FACTORS MAY INFLUENCE THEIR CLAIMS
One could write books on this. Factors which influence claims: money, power, prestige, greed, self-serving claims, need to depreciate others, need for attention, and so on. The list is long. I am amazed anyone would give such a broad topic: It is akin to evaluating the possibility of world peace, or even peace in the Middle East. A three paragraph paper is not going to hack it.
If you want to analyze TV and Radio, think on Bill O'Reilly, Nancy Grace, Rush Limbaugh, Fox News. Why in the world do those folks report the nonsense they do? Reason: Some folks believe them. So Credibility is in part what some believe. Thus a niche for Fox News. So in your analysis, you can include the psychology of not only what is reported, but who is the audience, and why they listen. I saw a weekly 'newspaper' at the grocery checkout stand last week, the headlines were "First Pictures from Heaven". This week the headline is "Guided Tour of Heaven". That paper sells enough to stay in business, as does Rush, Nancy, and Bill.
Again, the answer to your question is complex, and is not likely to be dealt with in a short paper.
PS: Don't forget all those "GutBuster" ads on TV. One wonders how anyone can believe them, but their products sell and sell.
Here are some sites which may be of help to you in writing this paper:
The Problem:
http://www.poynter.org/content/content_view.asp?id=1205
http://people-press.org/reports/display.php3?PageID=838
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http://www.worldnetdaily.com/news/article.asp?ARTICLE_ID=38398
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Evaluating:
http://www.leaonline.com/doi/abs/10.1207/s15567419cy2701_10
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http://com.miami.edu/car/miamibeach1.htm