How many of those are actually active participants? That would be much
more telling and accurate view of the amount of users on the site. An
inactive member (say someone who doesn't visit/post within the last
year) doesn't contribute anything.
Yes, good question. My simple stats is based on figures which are on Home page. There is no API (at least i don't know about it) to pick-up more information, and parsing of HTML is out of my skills.
On the one hand deleted and fully inactive members are calculated. On the other hand probably few dozens of people have more than one thousand posts. Adding average 1 post/member my guess we have about 10% of active members.