my first thought was..there is really no way to ever know..
but maybe there is!
I bet if we took the amount of sales for the Barry Rice book or the Peter D'Amato book, then double that number, it would be a fairly accurate number for the amount of CP hobbyists in the English speaking world..
assuming about half of CP hobbyists are "serious" enough to buy a CP book..which IMO is probably likely..
yeah, it would still be a guess, but an educated guess at least.
Scot