The Appreciation Index or AI is a measure of how much the audience enjoyed the programme. The score, out of a hundred, is compiled by a specially selected panel of around 5,000 people who go online and rate and comment on programmes.
The score of 82 is relatively low for Doctor Who, and represents the lowest score of this series so far. However, it is equal with several Series 8 episodes, and represents a solid score when compared to other TV shows.
[Source: Doctor Who News]