It’s been a while, but I’m still active. Tuerca8 is…
133
See a lot of you later today. Bye.
Okay, I’ll play along. That makes 134. Or so…
Checking in…is that 135?
Somewhere in the neighborhood of 136
Naturally, I did the latter.
I decided to take a 2% sample of usernames, in the following manner: I randomly generated a number from 1 to 50 (turned out to be 40, FWIW), and checked the profile of that poster to see if s/he was still active. Then I checked the profile of every 50th poster after that.
I didn’t have a good definition of ‘active’ going in, so I asked - has this person posted in the:
Last week?
Last 2 weeks?
Last month?
Last 2 months?
Last 3 months?
I figured that anyone not falling in one of those categories, was inactive by anyone’s standards. Also, I excluded posters from the period in which they’d registered - in other words, if they registered two and a half months ago, but didn’t post in the last two months, I just treated them as inactive, rather than considering them to have posted in the past three months. (I figure we’re not likely to see them again, so they’re not really active.) And banned posters are, by definition, inactive.
My sample was of 204 usernames; the (non-cumulative) distribution looked like this:
Posted within: # 95% confidence interval
Last week 26 833 - 1766
Last 2 weeks 8 1178 - 2221
Last month 9 1578 - 2720
Last 2 months 6 1851 - 3047
Last 3 months 5 2082 - 3316
IOW, if we define ‘active poster’ to be anyone posting within the past 2 weeks, we have a 95% chance that the true number of active posters is between 1178 and 2221. And so forth.
Those numbers are higher than I trust, but fortunately I broke things down one more way that may shed more light. But I’ve got to run errands, so that’ll have to wait until later.
Ooo Ooo Ooo don’t forget me
138???
139ish…
That’s pretty good work there, RT. (Having stats flashbacks.) 
But, don’t you think weighting the sample towards the more recent end would yield a higher number of more active posters? Just an idea.
Aah! NO STATS… I’m having SPSS/SAS flashbacks!
140!!!
That’s right, the Illuminati’s Law of Fives enters into it again.
:::waves hand:::
Still here, just worked to a frazzle and having 'puter problems!
Okay, that means I’m 141? Is that in dog years?
:::wanders away again:::
Veb
I am a doper…but not a pot smoker. So you better all like me because I am VERY new.
Nart Fack
The 142nd trumpet blows, and the Walls of Ignorance comes crumbling down.
143
45, if I’m counted after Tengu. 
Veb! I haven’t seen you in a while! Yay! The moustachioed librarian lives!
Another doper checking in. Don’t know what number I am.
I don’t follow you, Demo. Of course, that might be because I didn’t explain my methodology clearly enough.
If you look at the URL of a member profile, it looks something like http://boards.straightdope.com/sdmb/member.php?action=getinfo&userid=2852 (or exactly like this, if your username is Democritus :)).
My sample was the profiles with userids 00040, 00090, 00140, … , 10190. (When I took my sample, the most recent userid was 10196.) So it wasn’t weighted at all; I took every fiftieth userid beginning with 00040.
What I sampled for was, how recent was their last post? And as you can see, 26 posters in my sample had posted in the last week, another 8 hadn’t posted in the past week but had posted within the past two weeks, and so on.
I also looked at post count in a very superficial (but still useful) fashion; I’ll talk about that next post.
In my post above, one thing I didn’t mention was that I also looked at post count for each userid in my sample, though in a very primitive way: I noted whether each ‘active’ poster had more than, or less than, 20 posts. My thought was that someone with less than 20 posts wasn’t very active, no matter how recently they might’ve posted; their presence on the boards would still be negligible.
So if we add a threshold requirement of 20 posts as part of the definition of an ‘active’ poster, my table looks more like this:
Posted within: # 95% confidence interval
Last week 21 624 - 1475
Last 2 weeks 5 833 - 1766
Last month 3 961 - 1938
Last 2 months 3 1091 - 2108
Last 3 months 3 1222 - 2277
I think that a post count factor is a necessary part of a definition of ‘active’, so these numbers have more to do with what we’re really after, which is, “How many different posters would we run into, if we had time to read a good chunk of the active threads on every forum?” If someone registered in April, and posted last week, but their post count is 12 (I had a couple of cases like this in my sample), I could be a pretty active poster and still have no idea they exist.
I’m tempted to redo this, with the cutoff at 50 posts this time, but that depends on whether I find the time. But I’m confident that we have well beyond 500 ‘active’ posters, by any reasonable definition. IMO, having more than 20 pasts, and having posted in the past 2 weeks, is a pretty good definition, so I’d say we’ve probably got over 800 actives, and quite possibly over 1000. And they’re not all going to post to this thread.
I have been known to post occasionally