Wikipedia is the world’s largest encyclopedia and one of the most popular sites on the Internet. But who wrote all of that content? This site collects research done on answering that question.
The Gang of 500: Many prominent Wikipedians believe most of the content is written by a small core group, a Gang of 500, who mostly know each other and are familiar with Wikipedia rules and protocols. Jimbo Wales, Wikipedia’s founder, has argued this in speeches. He says Wikipedia is written by “a community … a dedicated group of a few hundred volunteers” where “I know all of them and they all know each other”. Really, “it’s much like any traditional organization.”
The Anonymous Horde: The opposing view is that Wikipedia is written by a swarm of anonymous Internet users, each contributing a sentence or a word, with a coherent encyclopedia emerging from the combined result of all these individually small efforts.
Wales did a study counting who made the most edits on Wikipedia. “I expected to find something like an 80-20 rule: 80% of the work being done by 20% of the users, just because that seems to come up a lot,” he’s explained in talks. (He’s presented this data in numerous talks but has not published any details as far as I know.) “But it’s actually much, much tighter than that: it turns out over 50% of all the edits are done by just .7% of the users … 524 people. … And in fact the most active 2%, which is 1400 people, have done 73.4% of all the edits.”
Skeptical, Aaron Swartz did further research measuring the amount of content contributed by each user, instead of simply the number of edits. He replicated Wales’ claims about edits, but found that counting characters, the vast majority of major contributors are unregistered and that most have only made a handful of contributions to Wikipedia. A larger replication of the study for publication is currently in progress.
Seth Anthony studied the patterns of various Wikipedia contributors, concluding: “Only about 10% of all edits on Wikipedia actually add substantive content. Roughly a third of those edits are made by someone without an account, half of someone without a userpage (a minimal threshhold for considering whether someone is part of the “community”). The average content-adder has less than 200 edits: much less, in many cases.” Anthony also found that none of the substantive edits were done by site admins who, upon investigation, used to contribute less frequently but more substantively, but who turned into “janitors” (Anthony’s term) after becoming admins.
A 2007 study by Kittur et al. attempted to replicate Swartz's results. They found a decreasing percentage of edits from admins and heavy users. However, using two new metrics they found continued strength in heavy user contributions. They did not provide any justification for their new metrics. They concluded that there was "a shift in the distribution of work from the elite  to the novice  users."
Denise Anthony, Sean W. Smith, and Tim Williamson did a study comparing "Good Samaritans" and "Zealots" of the French and Dutch Wikipedias to see whose edits survived (by counting the number of characters retained in the current version). They found survival rates among unregistered users fell as the number of edits increased while survival rates among registered users increased as number of edits increased. The study is marred by its focus on registration and edit counts, as well as bizarre terminology and methodology, but it seems to support the Anonymous Horde theory.
Aaron Swartz: Who Writes Wikipedia?
Please let me know if you have corrections, comments or additions. This page is written by Aaron Swartz. You can contact me at firstname.lastname@example.org.