The reality is that MA has limited appeal (2-5% of the population )and with more martial arts on offer than ever before aikido has less and less market share (20 or 600 dojo in my home town ). Crunching the numbers a while back (it what i do for a living in some ways)
I came to the conclusion that 38 was a reasonable bench mark for an average dojo size in my home town.
Tweaking factors are competitiion (number of other dojos), demographics, advertising, mobility of people etc... here are the numbers and rather weak conclusions for the curous
So, where were you when I was have a discussion with Lee Price about the number of Aikido practitioners in the world