The role of audience measurement is to estimate the number and type of people who have an opportunity to see or hear advertising in the media. Media planners, buyers and sellers use this information to inform their planning and to oil the wheels of commerce between them.
It has sometimes been said that everybody loves progress, but nobody likes change. This is as true for audience measurement as it is for much else. Given its technical nature, few people maintain a close interest in the subject. It makes headlines when something goes wrong or when a major change in method causes the numbers to change from those people are accustomed to.