Hiroaki Izumi wrote:
10% of the general population in an area will be seriously interested in martial arts.
10% of those will be interested in Aikido if there is a good selection of martial arts in the area.
25% of those will actually start Aikido.
10% of those who start Aikido will stay in it for the long term.
20% of those who stay in Aikido for the long term will want to become instructors.
20% of those who want to become instructors will end up with the resources, time, and freedom to start and maintain a dojo.
According to the martial arts industry mags I get, the demographics on who has any interest in training in the martial arts more like 1% of the population (this includes kids who are by far the bulk of the students in most martial arts schools. Aikido is usually different with the majority of students coming from the adult population. So the adult figure may be less than 1%).
Your other figures are pretty spot on I think.