Here’s a question you are unlikely to read in a marketing textbook: What is the single most important demographic a marketer can target? Preteens? Women ages 25 to 39? Baby boomers? Truth is, there is only one real demographic of any true economic consequence. Granted, it is narrow, and difficult to find. But of all demographic categories, the only one that matters is the buyer. It is the buyer, more than any prescribed label or category, who controls the success or failure of a product. It is the buyer who ultimately justifies the investment in media. So it’s …