Freethought & Rationalism Archive

aa5874 · 11-06-2008, 11:05 AM

If "absence of evidence" is not "evidence for absence", what is the "evidence for absence"?

Keith&Co. · 11-06-2008, 11:10 AM

Quote:

Originally Posted by aa5874

If "absence of evidence" is not "evidence for absence", what is the "evidence for absence"?

"Absence of evidence" IS "evidence of absence." For a given value of evidence.

If there are no elephants in my back yard, they will not leave any footprints. If there are no elephant footprints in my back yard, that is fairly good evidence that there have been no elephants in my back yard.

It's not incontrovertable evidence, but it is evidence.

aa5874 · 11-06-2008, 11:17 AM

Quote:

Originally Posted by Keith&Co.

Quote:

Originally Posted by aa5874

If "absence of evidence" is not "evidence for absence", what is the "evidence for absence"?

"Absence of evidence" IS "evidence of absence." For a given value of evidence.

If there are no elephants in my back yard, they will not leave any footprints. If there are no elephant footprints in my back yard, that is fairly good evidence that there have been no elephants in my back yard.

It's not incontrovertable evidence, but it is evidence.

So, the evidence for elephants or their footprints will be absent.

There were no elephants in your backyard can be considered true forever until there is some evidence, perhaps a photograph or a credible eyewitness.

Absence is indeed the evidence for absence.

AlexG · 11-06-2008, 11:31 AM

The evidence of the christian God's absence is the absence of every other God that humans have believed in...

Elijah · 11-06-2008, 12:28 PM

If the sample you are using is complete then yes, but if it’s incomplete like speaking for the past while only being able to sample the present then no. You can state that elephants haven’t been thru your yard recently but not ever.

Keith&Co. · 11-06-2008, 12:47 PM

Quote:

Originally Posted by Elijah

If the sample you are using is complete then yes, but if it’s incomplete like speaking for the past while only being able to sample the present then no.

it doesn't have to be complete, as long as we understand the limitations of the evidence and the qualifiers of the conclusion.

If asked if elephants have EVER been in my yard, yes i'd have to say it was beyond my ability to make a firm conclusion.

If asked if elephants ARE in my yard, i'd say it wouldn't take very long to make a firm conclusion.

If a given condition would, or could be expected to leave specific evidence, and we look for the evidence we would expect, and find none, then the absence of evidence must be accounted for in our conclusion, one way or another.

aa5874 · 11-06-2008, 01:25 PM

Quote:

Originally Posted by Keith&Co.

If asked if elephants have EVER been in my yard, yes i'd have to say it was beyond my ability to make a firm conclusion.

If asked if elephants ARE in my yard, i'd say it wouldn't take very long to make a firm conclusion.

If a given condition would, or could be expected to leave specific evidence, and we look for the evidence we would expect, and find none, then the absence of evidence must be accounted for in our conclusion, one way or another.

Now , if there were never any elephants in your yard, what evidence would you expect?

Elijah · 11-06-2008, 02:48 PM

Quote:

Originally Posted by Keith&Co.

it doesn't have to be complete, as long as we understand the limitations of the evidence and the qualifiers of the conclusion.

(If I’m following you) I think if the lack of evidence is your evidence then the sample has to be relatively complete. You can have limited evidence and speak about what is included in that evidence but you can’t say what isn’t included doesn’t exist without examining a complete sample.

If you read the first page out of a book you have solid evidence on what is included in the rest of the story but not on what is absent in the rest of the book.

Quote:

If asked if elephants have EVER been in my yard, yes i'd have to say it was beyond my ability to make a firm conclusion.
If asked if elephants ARE in my yard, i'd say it wouldn't take very long to make a firm conclusion.

Agree. Agree.

Quote:

If a given condition would, or could be expected to leave specific evidence, and we look for the evidence we would expect, and find none, then the absence of evidence must be accounted for in our conclusion, one way or another.

That’s fine if where you look gives you a complete picture of the evidence (or lack thereof) which is impossible regarding events in the past. (Unless the "condition" effects the whole world throughout time.)

Keith&Co. · 11-06-2008, 02:57 PM

Quote:

Originally Posted by aa5874

Now , if there were never any elephants in your yard, what evidence would you expect?

If asked if elephants have EVER been in my yard, yes i'd have to say it was beyond my ability to make a firm conclusion

patcleaver · 11-06-2008, 03:20 PM

http://www.overcomingbias.com/2007/0...e-of-evid.html

Quote:

by Eliezer Yudkowsky

Absence of proof is not proof of absence. In logic, A->B, "A implies B", is not equivalent to ~A->~B, "not-A implies not-B".

But in probability theory, absence of evidence is always evidence of absence. If E is a binary event and P(H|E) > P(H), "seeing E increases the probability of H"; then P(H|~E) < P(H), "failure to observe E decreases the probability of H". P(H) is a weighted mix of P(H|E) and P(H|~E), and necessarily lies between the two. If any of this sounds at all confusing, see An Intuitive Explanation of Bayesian Reasoning.

Under the vast majority of real-life circumstances, a cause may not reliably produce signs of itself, but the absence of the cause is even less likely to produce the signs. The absence of an observation may be strong evidence of absence or very weak evidence of absence, depending on how likely the cause is to produce the observation. The absence of an observation that is only weakly permitted (even if the alternative hypothesis does not allow it at all), is very weak evidence of absence (though it is evidence nonetheless).

11-06-2008, 11:05 AM	#1
aa5874 Contributor Join Date: Feb 2006 Location: the fringe of the caribbean Posts: 18,988	Absence of evidence If "absence of evidence" is not "evidence for absence", what is the "evidence for absence"?

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11-06-2008, 11:31 AM	#4
AlexG Junior Member Join Date: Aug 2008 Location: Southern California Posts: 12	The evidence of the christian God's absence is the absence of every other God that humans have believed in...

11-06-2008, 12:28 PM	#5
Elijah Veteran Member Join Date: Mar 2005 Location: MidWest Posts: 1,894	If the sample you are using is complete then yes, but if it’s incomplete like speaking for the past while only being able to sample the present then no. You can state that elephants haven’t been thru your yard recently but not ever.

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