So you type in a site into quantcast to look at the site's demographics and the information is pretty clear and straightforward for the most part. But one thing I don't understand is what exactly is the significance of the index. I mean, quantcast gives you a percentage of Caucasians or certain age group that make up the site's audience but how important is the index? I understand that the index tells you how much of a certain demographic you have for a particular website in comparison to other websites but how can this be useful. When setting up a campaign where I want to target certain demos, should I focus on the percentages or the index?