France is a country in which there is still a important presence of aikido, till the early 50's.
Due to sport structuration in the country, under the relevent Ministry, aikido is considerer as a sport (and this is not a discussion for this thread ). As a consequence, its aknowledged federations (currently FFAAA and FFAB, which are the far largest aikido groups to my knowledge) must indicate to the Ministry some data about them which are then publically released.
These communications - and questions about aikido attractiveness - have led me to publish, in French, an article about the demographic evolution of aikido in France till 2000 to 2015 in "Dragon magazine special aikido", a french review mainly dedicated to aikido. This paper had also been publish (into two parts) in my own blog : here (I) and here (II). A kind of update (for 2016) is published here.

Let me know your opinion about !

By the way, I have also (global) questions : is there any other country or organisation that have also such public data ? Where can I found them ? Thanks !