"The Return of Doctor Mysterio" had an Appreciation Index score of 82 - exactly the same as previous Christmas Specials "The Husbands of River Song" and "Last Christmas".
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.
The AI scores for Series 9 are below:
"The Magician's Apprentice" - 84
"The Witch's Familiar" - 83
"Under the Lake" - 84
"Before the Flood" - 83
"The Girl Who Died" - 82
"The Woman Who Lived" - 81
"The Zygon Invasion" - 82
"The Zygon Inversion" - 84
"Sleep No More" - 78
"Face the Raven" - 84
"Heaven Sent" - 80
"Hell Bent" - 82
"The Husbands of River Song" - 82
