This is mainly want they call a snowball survey. They interview a certain amount of people or through computers find average scores. It does not necessarily mean it is accurate. Take for instance the neilson's ratings for tv, it was done by having the family by that last name rate and determine what we watched. Thankfully this system I hope is no longer used as there are so many other people with a view. Basically, the statistics were formed by how many watched and so forth. The greater the number of viewers, the more like the show stayed on the air. Statistics will vary like I say, such as snowball surveys that just ask random people at random times. But real statistics are hard to find. Otherwise you would have to question every individual in existance