text: The leader in this space is Nielson Media Research - You'll find all the answers on their site including how they measure their audience, how they sign people up (random sample), etc.\n\nhttp://www.nielsenmedia.com/nc/portal/site/Public/menuitem.3437240b94cacebc3a81e810d8a062a0/?vgnextoid=130547f8b5264010VgnVCM100000880a260aRCRD