Nature has a special report at http://www.nature.com/news/2005/051212/full/438900a.html , detailing the results of an accuracy comparison between WP and EB. While the Wikipedia articles often contained more inaccuracies than Britannica's, they don't look at the article sizes in each case. With Maveric149's help, I did:
http://en.wikipedia.org/wiki/Wikipedia:Village_pump_%28news%29#Nature_follow...
Result: Average article size for Wikipedia: 6.80 KB; Britannica: 2.60 KB. Number of errors per 2KB for Wikipedia: 1.4; Britannica: 3.6.
Put another way: Wikipedia has 4 errors to their 3; our articles were also 2 1/2 times longer on average.
It's not 100% accurate, but I was only going for a ballpark estimate. Note: we copied the displayed WP text, not the edit box text, and removed the TOC, See also, references, external links, and any other big tables or lists. The WP text came from just before the Nature article was published.
brian0918