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"Absence of evidence isn't the evidence of absesence."

derchin

Critical Thinker
derchin
Joined
Apr 30, 2012
Messages
353
Or the "you can't prove/disprove X," argument. Used by some theists and atheists when defending their beliefs.

What do you make of it?
 
derchin said:
What do you make of it?
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Absence of evidence isn't evidence of absence... except where there is an absence of evidence in circumstances where evidence would reasonably be expected to be found.

For example, if there have been persistent rumors of a yeti living in a local forest for decades, the fact that nobody's managed to provide evidence of a yeti living there isn't evidence that there isn't one there.

But if you have hundreds of people systematically search the forest for evidence of a yeti and you find no evidence of a yeti in the forest, then this counts as evidence of absence of a yeti because you'd normally find some evidence of any large life forms living in the forest by that method.

(Also worth remembering: absence of evidence of presence may not be evidence of absence, but absence of evidence of absence isn't evidence of presence either.)
 
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derchin said:
Or the "you can't prove/disprove X," argument. Used by some theists and atheists when defending their beliefs.

What do you make of it?
Click to expand...

Johnny says: "This? Why, I can make a hat, or a brooch, or a pterodactyl..."
 
derchin said:
Or the "you can't prove/disprove X," argument. Used by some theists and atheists when defending their beliefs.

What do you make of it?
Click to expand...

It is, on the face of it, true.

Unfortunately people take the next step, which is "and therefore, you should judge it a possibility".
 
What I make of it is: the null hypothesis wins.

And, for the record, the null hypothesis is not "whatever the majority of people in my culture believe."
 
I've always been mildly disturbed by the assertion. I'll buy "absence of evidence is not proof of absence", but it really is evidence. It just always seemed obvious to me that the saying was wrong. You get home, you call your wife's name and get no answer, you check all the rooms and don't see her. You have an absence of evidence that she is home, which is pretty good evidence that she is not home, no? True, she could be in the attic, or perhaps dodging just ahead of you from room to room, or hell, maybe you're secretly Reed Richards, but it's likely she just isn't there, based entirely on the absence of evidence that she is.

Of course, I realize that's just sort of armchair reasoning, so it was with some delight a few years ago that it turned out I'm not the only one who feels this way, and others have expressed it far more rigorously than I have above. Turns out, I'm just a Bayesian.

http://lesswrong.com/lw/ih/absence_of_evidence_is_evidence_of_absence/
http://blog.sigfpe.com/2005/08/absence-of-evidence-is-evidence-of.html
 
Absence of evidence quite clearly is evidence of absence.

For example, if a murder was committed and you were accused of it then the fact that not a trace of you could be found at the scene would be provided as evidence that you weren't there and didn't do it.

It may not be conclusive evidence, but it is evidence. The strength of which is largely dictated by what we would expect to find.

Where it all gets silly is when the theist try to justify the absence of evidence.

'Of course he didn't leave any hair at the scene...he is able to shed all his hair at will and did so prior to entering the apartment.'

'Of course there are no footprints...he can levitate'

'Of course there is no DNA, he doesn't have any. In any case, he didn't need to enter the apartment. He could have killed him with the power of his mind'

'And how does that work?'

'Um..magic'

'Really?'

'You can't prove me wrong!!!!!!!!!!!!'
 
Brian-M said:
Absence of evidence isn't evidence of absence... except where there is an absence of evidence in circumstances where evidence would reasonably be expected to be found.

For example, if there have been persistent rumors of a yeti living in a local forest for decades, the fact that nobody's managed to provide evidence of a yeti living there isn't evidence that there isn't one there.

But if you have hundreds of people systematically search the forest for evidence of a yeti and you find no evidence of a yeti in the forest, then this counts as evidence of absence of a yeti because you'd normally find some evidence of any large life forms living in the forest by that method.

(Also worth remembering: absence of evidence of presence may not be evidence of absence, but absence of evidence of absence isn't evidence of presence either.)
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This, absence of evidence may not be proof of absence, but it certainly can be evidence.
 
Brian-M said:
...snip...

(Also worth remembering: absence of evidence of presence may not be evidence of absence, but absence of evidence of absence isn't evidence of presence either.)
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And if you can say that fives times fast then it is evidence of an absence of alcohol in your bloodstream! :)
 
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I'd even quite happily leave it at "Absence of evidence isn't the evidence of absesence," but with the caveat that absence of evidence is also no reason to assume that something exists. Yes, there is always some tiny chance that we just didn't look in the one hidden cave where the world's only yeti lives, or we didn't stumble upon the exact spot where the dimensional portal to Santa's workshop is, but in the meantime there is also no rational reason to believe in them without any evidence that requires a yet or Santa to explain.

Really, it's just Occam's Razor, and I think most people find it quite natural to apply it to anything except their pet woowoo.

E.g., if I told someone that mom is Wonder Woman and has an invisible airplane, they would want some evidence before they believe either. "You can't disprove that she has an invisible plane" may be technically correct, but it also doesn't mean any rational person should believe it just because lack of evidence for such an invisible plane isn't evidence of absence of said plane.

E.g., to take a sadly more real example, it was (and still is) impossible to prove that people don't fly on a broomstick to the witches' sabbath. You'd think that at least something like her husband testifying that she was at home in bed at the supposed night would be evidence that she didn't go anywhere, or that it was outside a major market and nobody there saw anyone flying or any window or door opening on that house, but they covered that aspect too: see, witches make themselves invisible, and leave a demonic double behind in bed. So really, the best you could have was a complete absence of evidence that such a sabbath exist or anyone goes there. But conversely, I think we can agree, that then there is no reason to assume that one does exist.
 
HansMustermann said:
I'd even quite happily leave it at "Absence of evidence isn't the evidence of absesence," but with the caveat that absence of evidence is also no reason to assume that something exists.
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Exactly. "Absence of evidence isn't evidence of absence" only works in conjunction with the Null Hypothesis. Given the divide between what actually exists and what could possibly exist, working from possible and trying to find reasons why it doesn't exist is, at best, inefficient.

But this is all rather academic. It's blatantly obvious when dealing with Theist and other Woo Slingers that it's not about evidence of absence versus absence of evidence. It's all about them coming up with various malarkey as to why they should just get to make crap up.
 
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