Halfaker, Geiger, Morgan, and Riedl have a new paper on this topic (pdf), here is the abstract:

Open collaboration systems like Wikipedia need to maintain a pool of volunteer contributors in order to remain relevant. Wikipedia was created through a tremendous number of contributions by millions of contributors. However, recent research has shown that the number of active contributors in Wikipedia has been declining steadily for years, and suggests that a sharp decline in the retention of newcomers is the cause. This paper presents data that show that several changes the Wikipedia community made to manage quality and consistency in the face of a massive growth in participation have ironically crippled the very growth they were designed to manage. Specifically, the restrictiveness of the encyclopedia’s primary quality control mechanism and the algorithmic tools used to reject contributions are implicated as key causes of decreased newcomer retention. Further, the community’s formal mechanisms for norm articulation are shown to have calcified against changes – especially changes proposed by newer editors.

This is an interesting paper, but I think it undervalues the hypothesis that potential contributors simply prefer to be in on things which are both new and cool. Wikipedia, which is no longer new, cannot be so cool. That is why Beethoven’s 5th does not top the pop charts, though if it were new it might.

For the pointer I thank David Siegel.