Richard Fernandez writes a grown up post about the NIE and ian Intentions:
Those worried the recent NIE is wrong in estimating that is no longer pursuing a nuclear weapons program have grounds to worry. Intelligence assessments are often wrong. That may not accord with the glamorous movie portrayals of spies and espionage, but that's how it is.Read the whole thing.
A list of historical intelligence failures makes depressing reading.
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Whether we like it or not, there are limits to what intelligence can know at any one time. The inescapable uncertainties may make it impossible to decide the status of ’s nuclear program "once and for all". As in the case of the Soviet Union changes in the situation and leadership happen all the time. Honest analysts must keep revising the picture as new information comes to light. While Washington politics describes any change in intelligence estimates as examples of ‘lying’ or incompetence the plain fact is that altering assessments is endemic to the process. An unchanging intelligence picture is a wrong picture. Changing your mind is a natural thing to do.
What’s needed is a way to keep improving the picture with each successive measurement. Bruce Blair, a former Senior Fellow at the Brookings Institution, notes that as long as “changing one’s mind” is done scientifically using a mathematical tool called Bayes’ analysis, the result is a more accurate intelligence estimate.
Bayes' analysis is often called the science of changing one’s mind. The mental process begins with an initial estimate – a preexisting belief – of the probability that, say, an adversary possesses weapons of mass destruction, or that an attack by those weapons is underway. This initial subjective expectation is then exposed to confirming or contradictory intelligence or warning reports, and is revised using Bayes' formula. Positive findings strengthen the decisionmaker's belief that weapons of mass destruction exist or that an attack is underway; negative findings obviously weaken it. … it is quite possible for the intelligence findings to be wildly off the mark for 10 or more cycles of assessment before settling down and converging on the truth.
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The key to achieving a "convergence" between fact and perception is repeated measurement. In plain words intelligence agencies must repeatedly measure and re-measure until they are convinced what they are seeing is "true".