A generation ago, consumers were at the mercy of advertisers who spoon-fed them marketing messages across a few media channels: print, billboards, television, radio. These advertisers created markets, defining and reinforcing consumer stereotypes. In the 1950s, advertising was primarily a one-way conversation with a captive audience. TV advertising grew and matured into a viable marketing medium. Experts were the style makers.
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Additionally, there are many situations where PPC (a component of SEM) makes more sense than SEO. For example, if you are first launching a site and you want immediate visibility, it is a good idea to create a PPC campaign because it takes less time than SEO, but it would be unwise to strictly work with PPC and not even touch search engine optimization.