I need some sources regarding the changes in the size of Buddhist populations since the death of Gautama Buddha, e.g. the number of Buddhists in what is modern day India from 410 BC until now, or just global historical data of Buddhist populations around the world since the religion started spreading. Exact sources would be great. This is part of a research paper I am doing, and partly out of pure curiousity as well. Thanks.
There's the Maps of Ancient Buddhist Asia and History of Buddhism mentions some population figures for certain eras, but I don't know of any detailed census data particular to Buddhism prior to the last couple of centuries.
For recent data, there's the PEW Religious Affiliation Report
Hope this helps in some small way.