Appreciation Index

The AI or Appreciation Index is a statistical representation of the amount of enjoyment the audience derived from a particular episode of television.

An "AI score" is calculated using a small, but representative, group of viewers. This sample will watch a program and then rate the program on a scale of one to ten. The scores are then averaged, and multiplied by ten. Hence, an AI of 67 means that 6.7 was the simple mean of all responses. Scores of 85 or better are rare, and thus considered "excellent". Scores below 60 are considered "poor". Scores for every episode of the BBC Wales version of the program — save The End of the World and Love & Monsters — have been 80 or above. Every story since Smith and Jones has achieved at least an 85 until Victory of the Daleks, scoring 84  making it almost 3 years of 85 AI. The highest-ever AI for a Doctor Who episode was a 91, received by both The Stolen Earth and Journey's End.

The Appreciation Index was the original method for determining the success or failure of radio and television programs in Britain, and has been employed by the BBC, in some form, since 1936. With the advent of commercial television, however, advertisers wanted to know how many people were watching. Ratings — a measure of the raw number of viewers in front of television sets — thus supplanted the AI as the primary measure of televised success. However, as the BBC is not a commercial enterprise, the AI still retains importance in determining the fate of television programs on the networks of the BBC.