Whereas regular ratings information can be calculated overnight, the AI of a programme can take up to two weeks to calculate, and is therefore not given the same prominence by the television industry in the UK. However, the AI can be useful in assessing the public's attitudes to programmes made for small or specialist audiences, especially in cases where ratings information on its own may be unreliable. If a television programme has performed passably in the ratings, yet achieves a high AI, it can help to determine whether the programme should be recommissioned.
The average AI for a drama programme on UK television channels BBC One and ITV1 is 77. A score of 85 or more is considered excellent, while a score of 60 or below is considered poor. Sometimes a programme will not garner an AI, as the response for that programme may have been too small. Nor is the AI a conclusive measure; while it is valuable for comparisons within a particular programme category, comparisons between the AIs of different programme types (e.g. dramas with quiz shows) carry no weight.
A flaw in the method became apparent when programmes with low audience numbers were left with a small, yet loyal, core of fans. These would give the programme an inflated AI. When commercial television launched in Britain in 1955, advertisers were less concerned about attitudes to programmes than they were about viewing figures, and this marked the start of the frequent measurement of audience totals. With the establishment of commercial television, individual broadcasters began to gather their own ratings data, as well as viewer opinion in the form of the AI, until 1981, when the major industry players set up the Broadcasters' Audience Research Board (BARB) to compile this information. In 2002, BARB ceased to compile AI data; as of January 2008, the BBC carries out its own research.
The results are used to calculate a score between 0 and 100. The viewing diaries come with questionnaire booklets which can be tailored to ask questions of specific programmes or series. The BBC in particular has used this service to gauge the attitudes of younger people towards its programmes, as well as what members of the public were doing when watching, and their moods.
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