In the new design, [[Special:Statistics]] has a field for the number of "active users", supposedly the number of unique usernames of logged-in users in the last 30 days of Recent Changes. However, this number is frozen at 10,263 for the English Wikipedia, 2551 for the German Wikipedia, and 233 for the Swedish.
On the IRC channel #wikimedia-tech, Siebrand believed that a shell user needs to run updateSpecialPages.php. Ialex added that this is probably done every 3 days.
Is there a way this could be done at more regular intervals, e.g. daily or hourly? It would be very interesting to see the number change over time as we try to recruit new contributors, and persuade existing ones to remain active.
If the window is 30 days ($wgRCMaxAge = 30*86400), it means that when a Saturday's (low) activity is added, the (high) activity of a Thursday four weeks ago is removed. That will cause an oscillation over the week, since all weekdays are not equal.
From a statistical point of view, 28 or 35 days would be a better
measurement window.