Absence of Evidence

[nemorathwald]

There's a saying: "Absence of evidence is not evidence of absence." Actually, it usually is.

If you were in this room, I would probably see you. You are not the sort of people to hide in rooms. The evidence of your absence is not totally conclusive, but what difference does that make?

"If you can't disprove what I say with absolute certainty, both alternatives carry equal weight." No, they do not. At all. Not even close.

Some things generate evidence by their presence. An unseen postage stamp in this room-- that's small enough that I can buy this argument. But if you say a full-size 747 jet plane is in this room, I would expect it to generate a metric ton of evidence. The bigger, brighter, noiser, or more active, the more this applies.

If you say it is an invisible and intangible 747, I would say that's not a 747. We really don't have to take this sort of thing on faith.

Comments

[sorcycat.livejournal.com]

Let me advocate for the devil a moment. The absence of evidence is not equal to the presents of refuting evidence.

[nicegeek.livejournal.com]

See Wikipedia's section on Distinguishing absence of evidence from evidence of absence.

[stormgren.livejournal.com]

You never know. It could be a ninja 747

[matt-arnold.livejournal.com]

I like this example from that page:

* One look in the back seat of one's car and finds no adult-sized kangaroos and then uses this negative/null adult-sized kangaroo detection results in conjunction with the previously determined fact (or just plain old proposition) that adult-sized kangaroos, if present, cannot evade such detection, to deduce a new fact that there are indeed no adult-sized kangaroos present in the back seat of said car.