Objectives
- Grade source reliability and information credibility separately
- Use the unknown grades honestly
Lesson
Two axes, kept apart, as in the NATO source-evaluation system often called the Admiralty code. A letter for the source — A completely reliable, B usually reliable, C fairly reliable, D not usually reliable, E unreliable, F cannot be judged. A number for the specific information — 1 confirmed by independent sources and logical in itself, down through probably true, possibly true, doubtful, improbable, to 6 cannot be judged.
Keeping them apart is the whole point. A reliable source can carry a doubtful claim, and an unreliable one can be right about a particular thing. Collapse the two into a single score and a source's reputation starts laundering individual claims. That is how one trusted channel can carry a fabrication all the way into a conclusion.
The unknown grades are not insults. F and 6 mean no basis exists for evaluation, which is frequently the honest answer early in a case. An investigator who never records an F or a 6 is not being rigorous; they are guessing and rounding.
Grade on the item, in the file, not in your head. A grade held mentally decays toward whatever the analyst concluded later.