It seems to vary fron day to day. Is that how it’s set up or is it just me?
It varies because people keep posting new threads in their battle against ignorance.
[ul]Not to be cute about it, but how could it remain constant? Some days more dopers log on than on other days. Some days the sun is out and they post silly stuff on MPSIMS and then it rains and they move to the Pit. Like life itself there are ebbs and tides on SDMB and who would want it any different? 
[/ul]
It varies buy a goodly number sometimes. Not just by new posts. Is the board cleansed from time to time?
TubaDiva must have been putting on her french maid outfit again and grabbing the dustbuster.
Reeder, we need hard data. What number are you looking at, and how does it change?
Do you see one day
Members: 23,148, Threads: 116,430, Posts: 2,116,674
and the next day
Members: 4,586, Threads: 832,238, Posts: 83,109
? That would indeed be odd.
I suspect it may have to do with what the defaults per forum are set at – one day, two days, ten days, or whatever. If you don’t note that you’re only seeing threads active in the last 48 hours, you may think that the older threads have gone where the woodbine twineth.
Uh, cite? And remember, a picture is worth a thousand words. 
At the moment of this posting there ia 8 threads (not counting the stickies) visable on this board. What is the minimum amount?
Reeder, please be more precise or else provide a link to the page. Are you saying that you see 8 threads on the main page of the ATMB forum? Or that there are only 8 threads in every forum of the SDMB?
If you’re speaking about the ATMB forum, and you mean that a forum home page has a different number of threads from one minute to another, the explanation is probably this:
Suppose I start from the board home page, http://boards.straightdope.com/sdmb/index.php , and click on the “About This Message Board” link. At the bottom of the thread list, you will see that vBulletin shows the number of threads using the ATMB forum default, which is showing threads for the last **2 (two)**two days.
Now I click the logo on the top of the page to go back to the board home page. This time I click on the “Comments on Cecil’s Columns” link. I see that vBulletin shows the number of threads using the CCC forum default, which is showing threads for the last 10 (ten) days.
While I am still on the CCC main page, I use the Forum jump at the bottom, change the drop-down list box to show “About This Message Board”, and click on The Go button. vBulletin will bring up the “About This Message Board” home page using the default from the Comments on Cecil’s Columns forum, and in the ATMB page you will now see the number of threads for the past 10 (ten) days. My second visit to “About This Message Board” is showing me more threads than my first visit.
Does this help clear up matters?
As another point of clarification, you should note that when people say board they mean something like the Straight Dope message board as a whole. A board can contain several forums. A forum is something like General Questions, or MPSIMS, or About This Message Board. And of course, a forum can contain many threads.
Ok. I am referring to the ATMB board. Now there isn’t but 4 threads. Why do threads drop off without being pushed off?
Probably for the reason Arnold stated above. Check out the “show threads from last X days” box at the bottom of the forum thread list. Dollars to donuts the change you’re noticing is the number of days getting reset from 10 to 2 to 1 (or whatever).
Reeder, you have your settings set to “board default” when it comes to number of days per forum. I know, I just checked. 
I have it set to “2 days” for all forums. I see more threads in ATMB. I count 7 threads, not counting the stickies.
ATMB apparenty defaults to “last day”. You can change your settings in your user CP, under “Edit Options”.