Are Facts and Statistics Documented?
When using facts, you should hold Web sites to the same standards of documentation as books and journal articles. In other words, insist that the Web site can back up what it says with sources.
Factcheck.org demonstrates the good practice of providing sources. The example below shows Fact of the Day, with a link to the U.S. National Center for Health Statistics. It also shows how each article provides sources. If you're not familiar with the sources cited, take the time to evaluate them, too.