This page is about the idea of straightforward media 'effects' - the idea that people will simply copy things they've seen in the media. For material on more subtle media influences see the role models and identity sections.
The whole problem with the media effects research is that it takes place in that depressing corner of 'communications' research which places more value on a veneer of 'scientific' method than it does on actually saying anything.
If these 'scientific' approaches were appropriate and found interesting things, that would be good. But they usually aren't, and don't. This is made worse by the fact that rubbish methodology seems to be very popular. See the Journal of Communication for some classic examples.
My book Moving Experiences (1995) was meant to be an exposé of how surprisingly bad the research on media effects is.
This argument got a mixed reception from the British press.
The main argument of Moving Experiences is distilled in the article Ten Things Wrong With the 'Effects Model', the full text of which appears here.
You can also read the full text of the article 'Ruination once again' - Cases in the study of media effects by Tom Gormley.