The results are in…
97% of Wikipedia vandalism is by anonymous editors.
Here’s the scoop…
Vandalism Statistics and Methodology
Vandalism Study 1 (the first of many), analyzed 100 randomly selected articles for the months of November 2004, 2005, and 2006. For this period, these articles contained 668 edits, with 31 instances of vandalism. Therefore (admitting the small sample size) the study suggests 4.64% of edits are some form of vandalism.
Obvious vandalism…83.87% (26 out of 31 cases)
Deletion vandalism…9.68% (3 out of 31)
Linkspam…6.45% (2 out of 31 cases)
For more on these definitions and methodology, read the study details.
The study found that 25.81% of vandalism is reverted by anonymous users (8 out of 31 reverts), and 74.19% is reverted by Wikipedians with user accounts (24 out 31 reverts).
According to the study, the mean average time to revert a vandalism is 758.35 minutes (12.63 hours). Accounting for outliers, the median time to revert a vandalism is 14 minutes (based on these data points: 0, 0, 0, 1, 1, 3, 4, 4, 6, 7, 8, 10, 11, 11, 13, 14, 18, 23, 29, 51, 104, 222, 452, 490, 895, 898, 963, 1903, 2561, 6816, 7991).
How This Relates to ValueWiki
The question of whether to allow anonymous IP’s to edit Wikipedia is a perennial debate. I am following the Wikipedia Vandalism Studies like a hawk to determine best practices for ValueWiki. Currently, our ban policy is nearly identical to Wikipedia’s. But if we can determine better statistics for what percentage of anonymous edits are helpful, we may force users to register.
In fairness, I have to admit we are currently pleased with our anonymous contributions on ValueWiki. But it may be worthwhile to spend a month requiring editors to register, to determine if this encourages or discourages new users to sign up.