Wikipedia really is written by the public -- if this tremendously important bit of research is independently confirmed, it upsets conventional thinking.

Wales seems to think that the vast majority of users are just doing the first two (vandalizing or contributing small fixes) while the core group of Wikipedians writes the actual bulk of the article. But that's not at all what I found. Almost every time I saw a substantive edit, I found the user who had contributed it was not an active user of the site. They generally had made less than 50 edits (typically around 10), usually on related pages. Most never even bothered to create an account.

To investigate more formally, I purchased some time on a computer cluster and downloaded a copy of the Wikipedia archives. I wrote a little program to go through each edit and count how much of it remained in the latest version. Instead of counting edits, as Wales did, I counted the number of letters a user actually contributed to the present article.

If you just count edits, it appears the biggest contributors to the Alan Alda article (7 of the top 10) are registered users who (all but 2) have made thousands of edits to the site. Indeed, #4 has made over 7,000 edits while #7 has over 25,000. In other words, if you use Wales's methods, you get Wales's results: most of the content seems to be written by heavy editors.

But when you count letters, the picture dramatically changes: few of the contributors (2 out of the top 10) are even registered and most (6 out of the top 10) have made less than 25 edits to the entire site. In fact, #9 has made exactly one edit -- this one! With the more reasonable metric -- indeed, the one Wales himself said he planned to use in the next revision of his study -- the result completely reverses.

I don't have the resources to run this calculation across all of Wikipedia (there are over 60 billion edits!), but I ran it on several more randomly-selected articles and the results were much the same. For example, the largest portion of the Anaconda article was written by a user who only made 2 edits to it (and only 100 on the entire site). By contrast, the largest number of edits were made by a user who appears to have contributed no text to the final article (the edits were all deleting things and moving things around).

When you put it all together, the story become clear: an outsider makes one edit to add a chunk of information, then insiders make several edits tweaking and reformatting it. In addition, insiders rack up thousands of edits doing things like changing the name of a category across the entire site -- the kind of thing only insiders deeply care about. As a result, insiders account for the vast majority of the edits. But it's the outsiders who provide nearly all of the content.

And when you think about it, this makes perfect sense. Writing an encyclopedia is hard. To do anywhere near a decent job, you have to know a great deal of information about an incredibly wide variety of subjects. Writing so much text is difficult, but doing all the background research seems impossible.

On the other hand, everyone has a bunch of obscure things that, for one reason or another, they've come to know well. So they share them, clicking the edit link and adding a paragraph or two to Wikipedia. At the same time, a small number of people have become particularly involved in Wikipedia itself, learning its policies and special syntax, and spending their time tweaking the contributions of everybody else.

Other encyclopedias work similarly, just on a much smaller scale: a large group of people write articles on topics they know well, while a small staff formats them into a single work. This second group is clearly very important -- it's thanks to them encyclopedias have a consistent look and tone -- but it's a severe exaggeration to say that they wrote the encyclopedia. One imagines the people running Britannica worry more about their contributors than their formatters.

And Wikipedia should too. Even if all the formatters quit the project tomorrow, Wikipedia would still be immensely valuable. For the most part, people read Wikipedia because it has the information they need, not because it has a consistent look. It certainly wouldn't be as nice without one, but the people who (like me) care about such things would probably step up to take the place of those who had left. The formatters aid the contributors, not the other way around.