Evaluating sources of information...

Everyone should be reviewing the sources of information they use to make decisions. Whether it is for whom one votes in an election or which refrigerator one buys, one should use all available tools and reasoning to discern the best information so that one can take the most favorable course of action. Look back at your life and honestly answer yourself as to how many times you would have been better served to have just smiled, nodded and ignored advice because the bearer of that advice was not in a position to know and/or completely unreliable as a source of information. I think you'll see just what I mean. Of course, we do judge reliability from experience with a source and sometimes it takes some time before we discover that some people are simply liars. Still, as in all things, one must do the best one can with what's available.

Intelligence source and information reliability rating systems are used in intelligence analysis.
A system commonly employed rates the reliability of the source as well as the information. The source reliability is rated between A (history of complete reliability) to E (history of invalid information), with F for source without sufficient history to establish reliability level. The information content is rated between 1 (confirmed) to 5 (improbable), with 6 for information whose reliability can not be evaluated.
For example, a confirmed information from a reliable source has rating A1, an unknown-validity information from a new source without reputation is rated F6, an inconsistent illogical information from a known liar is E5, a confirmed information from a moderately doubtful source is C1.
The evaluation matrix as described in the Field Manual FM 2-22.3:

Source reliability

	Rating	Description
A	Reliable	No doubt about the source's authenticity, trustworthiness, or competency. History of complete reliability.
B	Usually reliable	Minor doubts. History of mostly valid information.
C	Fairly reliable	Doubts. Provided valid information in the past.
D	Not usually reliable	Significant doubts. Provided valid information in the past.
E	Unreliable	Lacks authenticity, trustworthiness, and competency. History of invalid information.
F	Cannot be judged	Insufficient information to evaluate reliability. May or may not be reliable.

Information reliability

	Rating	Description
1	Confirmed	Logical, consistent with other relevant information, confirmed by independent sources.
2	Probably true	Logical, consistent with other relevant information, not confirmed.
3	Possibly true	Reasonably logical, agrees with some relevant information, not confirmed.
4	Doubtfully true	Not logical but possible, no other information on the subject, not confirmed.
5	Improbable	Not logical, contradicted by other relevant information.
6	Cannot be judged	The validity of the information can not be determined.