"Before the Flood" had an Audience Appreciation Index (AI) score of 83. The AI scores so far this series are:
"The Magician's Apprentice" - 84
"The Witch's Familiar" - 83
"Under the Lake" - 84
"Before the Flood" - 83
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.
There's a weird kind of consistency developing so far this series - with part one of a story scoring a point higher than part two.