Islam is the fastest shrinking religion in the world. The latest Gamaan survey of Iran, with 39,000 valid responses out of 50k, shows less than 40% self identify as Islamic.
The study is believed to be the largest since the Iranian revolution.
It seems the Islamic revolution has killed off Islamic followers!
Notably, Christianity is not picking up al the ex-muslims!
The survey results are available here: GAMAAN-Iran-Religion-Survey-2020-English.