Demographics are the DNA of marketing: age, sex, income, profession, marital status, location, and so on. Advertisers rely on demographics to help decide which sites are most likely to help them reach their specific audience. Knowing your audience demographic not only helps you sell ads, it also lets you know who your users are and what they want. To figure out your own site's demographics, download a copy of SurveySolutions, cobble together a survey, and post it on your site.