Degradation of Television

Teen son is working on an essay for his Regina Coeli class and is having trouble with his research. I'm hoping that one of you can help. He is writing about the decline of television since it's inception. In searching the Internet, he's found commentaries on the phenom, but he's looking for research. Something that he can cite as a resource that lays out the shift from wholesome family fare to low-life scum fare. (Am I showing my prejudice against TV?) Perhaps a study or two not only on the shift but its affect on our culture.