In a comparison of 42 articles from the two sources, covering a broad swath of the scientific spectrum, the respected journal Nature found little disparity in accuracy.

The findings were published in an online article on Wednesday which, according to its author, was the first time peer review had been used to compare the two encyclopaedias.

Jimmy Wales, who founded Florida-based Wikipedia in 2001, said: "We're very pleased with the results and we're hoping it will focus people's attention on the overall level of our work, which is pretty good."

Experts who reviewed the articles found that the average scientific entry in Wikipedia contained four errors or omissions, while Britannica had three.

Such errors appear to be the exception rather than the rule, Nature said. Of eight "serious errors" the reviewers found - including misinterpretations of important concepts - four came from each source, the journal reported.

Recent criticism

The findings are a boost for Wikipedia, which has been criticised over some rogue entries recently.

Two weeks ago John Seigenthaler Sr, an American journalist,  complained that a Wikipedia entry incorrectly named him as a longtime suspect in the assassinations of president John F Kennedy and his brother, Robert.

The author of the entry, which had been running for four months, Robert Chase, apologised. He said he posted the article in order to trick a colleague.

As a result of the prank Wikipedia changed its policy so that only registered users could create entries. And next month the encyclopaedia plans to begin testing a new mechanism for reviewing the accuracy of its articles.

The group also is working on ways to make its review process easier to use by people who have less familiarity with computers and the internet.

Wales said the accuracy of his project varies, depending on the topic. The site's stronger suits include pop music and technology. That is because Wikipedia's stable of dedicated volunteers tend to have more collective expertise in such areas, he said.

The site tends to lag when it comes to subjects touching on the humanities, such as the winner of the Nobel Prize for literature for a particular year.

Speed and breadth

Encyclopaedia Britannica officials declined to comment on the findings. But Tom Panelas, a spokesman, did say that such comparisons, if conducted correctly, are valuable "because they tell us things you wouldn't know otherwise".

Some Britannica officials have publicly criticised Wikipedia's quality in the past. But Panelas praised the free service for having the speed and breadth to keep up on topics such as "extreme ironing", the sport, in which competitors iron clothing in remote locations.

Britannica researchers plan to review the Nature study and correct any errors discovered, Panelas said.

Unlike Britannica, which charges for its content and pays a staff of experts to research and write its articles, Wikipedia gives away its content for free and allows anyone - amateur, professional, expert or novice - to submit and edit entries.

The site, which has 3.7 million articles in 200 languages, is the 37th-most visited on the internet, according to the research service Alexa.