The Encyclopaedia Britannica Internet Guide:

How are sites selected and rated?

Britannica editors judge candidate sites according to a balance of the following criteria:

• accuracy, completeness, and utility of information and effectiveness of presentation
• credentials and authority of the author or publisher
• of design and ease of navigation
• frequency of revision
• quality of graphics or multimedia

About 85% of the 65,000 in the Britannica Internet Guide receive a Noteworthy rating. These include (a) informational sites which, in the judgment of the editors, will be useful to readers but which have a limited scope or little or no editorial enhancement; (b) works of art and literature, historical documents, and other primary resources; and (c) many official sites for corporations, schools, libraries, newspapers, magazines, and other institutions. Although these sites are not awarded a star in this selective guide, they should still be regarded as valuable sources of information.

About 15% of the sites receive a Recommended (one star) rating; less than one percent are judged Exceptional (two stars); and about 40 are designated Best of the Web (three stars). The sites that receive high ratings from Britannica editors typically demonstrate significant editorial effort and enhancement, present quality information through an elegant and efficient design, provide up-to-date coverage for time-sensitive topics, and exhibit well-designed graphics and multimedia when such features are appropriate. These sites also tend to include a substantial amount of broad-based original content on their subjects, although directories and sites that are more narrowly focused but are of exceptionally high quality may also receive high ratings.

While the editors seek to include only quality sites that provide reliable information, the accuracy of every statement at every site cannot be guaranteed.