Minimum Inclusion Criteria
We only include sources that are believed to be authoritative, accurate, credible and generally respected by peers.
Sites must be free, open access, user-friendly and accessible with all browsers and operating systems.
Most Desired Criteria
We prefer sources that are peer-reviewed and unbiased.
Preference is given to educational institutions, nonpartisan government agencies and non-profit organizations.
Exclusion Criteria
We exclude sources that are inaccurate, heavily biased and user-hostile.
Sources that are closed access, fee-based or require proprietary software to view are excluded.
Safety Criteria
To further protect our visitors, we check the Google PageRank and SiteAdvisor Rating of all our sources.
Incoming links and outgoing links are checked for quality and relevance.
Text Ads
Text ads that appear in search results are dynamically generated by a third-party provider.
They are outside the scope of these standards.