"Under the Lake" had an Audience Appreciation Index (AI) score of 84. The AI scores so far this series are:
"The Magician's Apprentice" - 84
"The Witch's Familiar" - 83
"Under the Lake" - 84
The Audience Appreciation Index (AI) is a score out of 100 which is used as an indicator of the public’s appreciation for a show. Over 90 is considered exceptional, 85 or over is excellent, 60 or less is poor, and less than 55 is very poor.
Figures also show that over 1 million watched "Under the Lake" on catch-up on Sunday, raising the viewing figure from 3.70 million to 4.75 million.