La religion de Scientologie a été fondée par Ron Hubbard. La première église a été établie aux États-Unis en 1954. Depuis lors, le Scientologie s’est développée et compte plus de 7500 églises, missions et groupes et plus de 10 millions de membres dans 164 pays.(More than 7,500 churches, missions, and groups, and more than 10 million members in 164 countries.)
Now the 10 million figure (growing from 8 million a while ago) is most probably an inflated one, but the 7,500 figure for the various type of Scientology organizations around the world should be something that could objectively be verified.
If true and if you count an average of 10 members by organization, that would make the total figure to 75,000. Let's be generous and say there really are 20 per organization on average, that would bring us to 150,000, which I think is a relatively fair representation. Make that 300,000 and you probably won't be far off from the truth.
Back in the 1970's, when I believe the number of people attending courses was higher than it is now, we indeed had maybe 20 to 40 persons regularly attending courses in the average-sized organization where I was staff. However, we did have a "central file" of more than 2,000 persons to whom we would mail promotional material from time to time. If now you multiply 7,500 by 2,000, of course you get a figure of 15 million.
The CoS probably takes its 10 million figure from something like the central file, but it really is not very representative. The central file is made of every person who ever gave their address to the CoS, either buying a book or even just taking the personality test. Their address would probably be pulled out from the file if they write back asking for it, but if they just throw the promotional literature they receive in the garbage, their address would still be there and counted among the 10 million.