I'm interested in historical trends in religion and wondered if anyone knows of any reasonable sources of data on the number of adherents, for any/all different religions, throughout human history.
Obviously, older numbers would be very approximate estimates - and modern numbers would also likely be rough, given that this is a personal matter and somewhat sensitive in some parts of the world.
Does this information get included in census data - or has it ever been in the past? Do you know of any sources of data on this, even for single periods or religions, that I could use to piece together a fuller picture?
I know about this, which is great, but fairly recent and major religions only. Anything older, covering more religions?