Science articles in Wikipedia, the free online resource, are about as accurate as those in Encyclopedia Britannica, Nature magazine says.

The British publication had independent reviewers assess the accuracy of 42 pairs of articles from both encyclopedias.

Novices, experts and professionals all voluntarily submit or edit articles for Wikipedia. Britannica, meanwhile, charges for content and pays staff to research and write articles in the established resource.

Reviewers assessed a range of scientific articles from both resources, from Dolly the Sheep to Creutzfeldt-Jakob disease and Archimedes' principle on buoyancy.

"Only eight serious errors, such as misinterpretations of important concepts, were detected in the pairs of articles reviewed, four from each encyclopedia," the journal said.

"But reviewers also found many factual errors, omissions or misleading statements: 162 and 123 in Wikipedia and Britannica, respectively."

Since Wikipedia was founded in 2001, it has collected close to two million articles, including more than 850,000 in English.

Wikipedia has been criticized for posting a phoney entry purporting to be a biography of John Siegenthaler, a retired journalist who was an aide in the 1960s to attorney general Robert Kennedy.

"For a brief time, he was thought to have been directly involved in the Kennedy assassinations of both John, and his brother, Bobby. Nothing was ever proven," the joke entry said.

Wikipedia's publishers have introduced registration to try to discourage abuse. Its open-source policy remains in place.

Nature's reviewer said Wikipedia articles were often poorly structured and confusing, giving undue prominence to controversial theories.

Wikipedia posted a notice calling for contributors to correct errors and said it was working to make its review process easier for those less familiar with computers and the internet.

A spokesperson for Encyclopedia Britannica said they would review the magazine's findings and correct errors.

A Nature editorial calls on its readers to help improve Wikipedia entries by checking for errors or key omissions and fixing them, to make the site a "comprehensive, accurate and up-to-date reference work that can be accessed free from Manhattan to Mongolia."