National History Standard #4C discusses historical research capabilities and states that "students should be able to interrogate historical data by uncovering the social, political, and economic context in which it was created; testing the data source for its credibility, authority, authenticity, internal consistency and completeness; and detecting and evaluating bias, distortion, and propaganda by omission, suppression, or invention of facts".
Students need to approach any source - contemporary or historical; primary or secondary; print, nonprint or electronic as well as human - with a set of criteria to analyze the information presented. Robert Harris presents such an approach, although developed for looking at Internet sources, that is also applicable to analysis in general. It is called the CARS Checklist (Credibility, Accuracy, Reasonableness, and Support (10). He created this system to remind people that source evaluation - the determination of information quality - is an art based on inferences from a collection of clues.
Credibility - capability of being believed or trusted: What about this source makes it believable? How does the source know the information? Why should I believe this source over another? Elements to look for here are the author's credentials (education, training, and/or experience). If the author is an organization, what kind is it - corporate, governmental, non-profit? Is there evidence of quality control? Peer review, approval by members of the organization, review by an editor, etc. Most traditional media (books, magazines, organizational documents) usually have to meet some kind of approval of content before being made public.
Accuracy - correctness: Is this source factual, detailed, exact, comprehensive? Is it up-to-date or is currency relevant? Are important facts and other information deliberately left out? Did the creator invent information? Who is the audience for the source and what is the purpose - to inform or to persuade? Students should be alert to an air of carelessness and look carefully for dates, vague generalizations, and a very one-sided view that does not acknowledge opposing views or respond to them.
Reasonableness - fairness, objectivity, moderateness, and consistency: Is the information balanced (even the opponent's claims should be presented accurately), reasoned, fair? Is there a conflict of interest? Is the information really likely, plausible or possible? This is difficult for any researcher with a limited content background but every effort should be made to use previous and accumulated knowledge in a way that helps evaluate new information. Does the information make sense? Are there inconsistencies or contradictions?
Support - corroboration: Where did the information come from? Are sources listed? Is there a bibliography or other documentation? How does the author know what she/he knows? Do other sources agree? Don't take anything at face value. Cross-check each piece of information and compare with others.
It is very important for students to remember that every source is biased in one way or another. A source tells us only what its creator thought happened or wants us to think happened. Students should also consider how the source was created - routine or spur-of-the moment? Was it intended to be published?
Another area of consideration is when the document was created. Is it part of the event? Is it an account created at the time by firsthand observers or participants? Was it created after the event (still by firsthand observers or participants)? Was it created by someone not a participant but using interviews or evidence from the time of the event?
Students should be skeptical about every source found, just as historians are. Additional questions to ask: What may we never know? How can we find out about those people whose voices do not appear anywhere? Who preserved this piece of information and why? Do sources contain conflicting information and if so, how can it be evaluated?