“Absence of evidence isn’t evidence of absence”

An interesting column from Errol Morris on evidence, using the logic of Martin Rees with respect to the existence or not of extraterrestrial life (“absence of evidence isn’t evidence of absence”) to the question during the Bush Administration on whether or not weapons of mass destruction existed or not.

Part of the evidence vs anecdote challenge. Public service evidence on macro-trends can conflict with anecdotes from the political level, but the political level could also argue that the absence of evidence in our studies and research did not mean it did not exist. But still, better to operate with as sound evidence as possible:

What do I take from this? To me, progress hinges on our ability to discriminate knowledge from belief, fact from fantasy, on the basis of evidence. It’s not the known unknown from the known known, or the unknown unknown from the known unknown, that is crucial to progress. It’s what evidence do you have for X, Y or Z? What is the justification for your beliefs? When confronted with such a question, Rumsfeld was never, ever able to come up with an answer.

The Certainty of Donald Rumsfeld (Part 4) – NYTimes.com.