# Is absence of evidence evidence of absence? **URL:** \ **Category:** Great Debates\ **Created:** [February 20, 2010, 1:18am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720 "2010-02-20T01:18:27Z")\ **Posts on this page:** 20\ **Page:** 6
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [March 5, 2010, 6:56pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/101 "2010-03-05T18:56:57Z")
Let’s break it down: Absence of Evidence [for aliens] is Evidence of Absence [of aliens] Basically… Absence of evidence for aliens means no aliens _exist._ OR Absence of Evidence _of_ elephants, means no elephants _exist._ Clearly this is wrong. Now here’s where the elephant in the room presents some confusion: The problem with the elephant analogy, is it’s in a defined, closed space that can be thoroughly checked for everything we already know about an elephant and what kind of evidence an elephant would present. _Seeing_ that there is no elephant _is_ evidence. So, in this case, there is no “Absence of Evidence”. Seeing alone counts, because the room is small, and it’s obvious an elephant can’t be in it. It’s not a question of _existence,_ it’s a question of _presence._ Compare this to the aliens analogy, where the parameters of the investigation are in an _open_ universe, beyond the reach of man in many, many ways. Also, we’re not exactly sure what kind of evidence to look for, because we know nothing about these hypothetical aliens. So, we truly have absence of evidence, not only because we have none at all, but because we _know_ we cant reach the places we need to look for evidence, whether it’s there or not. This is _both_ a question of existence, and obviously, the question of presence becomes moot. But because we can’t look sufficiently and exhaustively for evidence all over the known universe, doesn’t mean they’re not out there (wondering if we exist). ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 6, 2010, 12:34am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/102 "2010-03-06T00:34:34Z")
> [@Jackmannii](#): > > What might be acceptable in a courtroom and what’s acceptable in the realm of science are two considerably different things.Anecdotes and personal “testimony” are a potential trigger for research, but they don’t constitute evidence.It becomes believable at a point where a defect is found that causes such a problem. Otherwise it’s likely part of a well-established pattern in which people step on the wrong pedal and panic, or get floor mats or other objects wedged into pedals producing unwanted acceleration. > > You could find millions of people who believe in alternative cancer remedies like laetrile, [the Hoxsey formula](http://en.wikipedia.org/wiki/Hoxsey_Therapy) or zapping oneself with an electric device, and all sorts of [testimonials](http://www.yesyoucansayno.com/testimonials.htm) supporting these things, and it all boils down to self-delusion and bunkum, not evidence. We’re cutting semantics and it is a distinction without a difference. If you want to call only reproducible, well documented, rigorously tested events as the only acceptable form of evidence, have at it. I doubt you’d find many others who would agree with you. If anecdotes and other testimony aren’t evidence, what are they? What do you call them? If I see a tree laying on the ground in the forest I’ll call that evidence the tree fell over, despite the fact that no scientist was there to study it, measure it and record the exact details of what happened. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 6, 2010, 12:42am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/103 "2010-03-06T00:42:45Z")
> [@Voyager](#): > > But if there were no dead mouse in the box, would you call the evidence that the box is there misleading? I don’t see why you would, so I don’t agree that the presence of the box gives evidence for the mouse. It just leads to a situation where the presence or absence can’t be determined. If the probability of a dead mouse goes from 0 to non-zero based on the presence of a box, what do you call the presence of the box? My personally definition of evidence is anything that strengthens a hypothesis should be considered as evidence in favor of that hypothesis. Is that a wrong definition? Sure, it can never be determine absolutely one way or another, and the probability of a dead mouse is exceedingly low, given no other knowledge. I’d be quite comfortable saying the chances are close enough to 0 for me consider it 0. Pretty much like how I consider my chances of winning the lottery, and I don’t even buy tickets. > [@Voyager](#): > > In your first case, then, the absence of evidence is indeed evidence of absence. Agreed. > [@Voyager](#): > > In your second case it isn’t, because the expected evidence is the same for the mouse in the box case and the mouse not in the box case. Given the extraordinarily unlikely event that a random box in a random room has a dead mouse and seeing no other evidence for the presence of mice, I’d quite comfortably assume no dead mouse. In other words, in this case I’d also go with absence of evidence if evidence of absence. I can’t know for sure, but I’m okay with that. ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [March 6, 2010, 1:13am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/104 "2010-03-06T01:13:44Z")
It’s increasingly difficult to care about the “Aliens! ALIENS!” argument, which is merely a gigantic bait and switch for the situations that the abscence-of-evidence argument is actually used. Yes. We’re all aware that if you look in your backyard and don’t find an elephant that tells you very little about the presence of elephants on the plains of Africa. That’s nice of you to point it out. Congratuations, you have achieved complete victory. Go out and have a drink on yourself. Tell all the other bar patrons how awesome you are. In _reality_, the reasoning supporting “absence of evidence is evidence of abscence” is three-pronged, and often more than one of them apply: 1. The God people’re arguing about supposedly _is_ in my backyard. Doing things. Changing things. So expecting to see fingerprints from the hand of God is not just perfectly reasonably, it’s the _only_ scenario that’s compatible with the God’s claimed nonfictionality. 2. The God people’re arguing about supposedly is without precedent in our reality, and in fact may be **literally impossible** based on what we know about our reality. Miracles, what? Infinite power? Energy not conserved? What the hoo-ha? (And you’re analogizing them with things that can and _do_ exist, now?) 3. The God people’re arguing about sounds completely made up, as best we can tell. Does anything anyone can make up suddenly merit automatic belief? By the way, you have an intense and overriding moral obligation to give me money. You can’t disprove this, obviously, so bring on the cash! Counters to the above three arguments. 4. If we’re not talking about any god that anyone cares about or worships, then this doesn’t apply. However, the only people who argue about gods that nobody cares about are militant agnostics, who think they’re making some kind of grand point when they point out that something irrelevent may exist! Whee. White noise, people. 5. This is the “it’s external to the universe/hidden inside the closed box” argument, and admittedly, there _might_ be something outside the Matrix. That doesn’t make analogizing to to aliens any less fraudulent of an argument - we at least know that sentient organic things _can_ exist. Even analogizing it to _radio_ is fraudulent - sure at one time we were unaware of radio, but nobody really postulated it before there was a reason to believe it. Cases where things are completely made up without evidence or any sort of precedent that turn out to be real anyway are _really_ thin on the ground - and they’re the _only_ things that analogize in any genuine way. And personally, I can’t think of a single example. 6. . . . I can’t think of a counter to this. People make stuff up. Such things don’t merit belief. Sure, such things aren’t _proven_ to be untrue…except in people’s normal use of the word. Things that are made up _start_ at zero credibility. Zero belief. Certainty of falsehood. Would evidence of plausibility for the story be evidence in favor of plausibility of the story? Of course. But we’re explicitly talking about a complete _abscence_ of such evidence here. And given that, it’s not _proof_ of falsehood, but you’re still at the initial position of absolute doubt anyway. Presuming you’re not a sucker, anyway. Could something evade all three arguments? Actually, er, no. Because to evade argument 3, you have to not sound like you’re pulling the entity in question from your rectal region. But to pull that off, there needs to be some basis in reality for believing it’s not made up - which _necessarily_ implies objective evidence, subjecting it to criticism 1. So you get it either coming or going - all three counters cannot apply simultaneously. To recap, lets try elephants and aliens again. An elephant can theoretically exist, and has been _practically_ shown to exist, so the bar for belief set by argument 2 is very low. But the expectation for elephants to leave behind evidence is very high, so argument 1 kicks in - if there’s an elephant in the area we expect to notice it, and if we don’t notice it, it’s not there. Aliens: Aliens have a moderate to low bar set for them by argument 2, since living organisms have been observed to exist on planets. (The credibility is better if you don’t limit yourself to the known, uninhabitable planets.) But then the tussle between 1 and 3 comes into play: if the aliens are probing people, why is the evidence for them so shaky? If the aliens are staying home, why shouldn’t I think they’re just made up? There’s no _actual_ reason to believe in them, unless you want to make statistical arguments for them - which is presenting evidence, in defiance of the ‘abscence’ rule. God. The bar set by criteria 2 is at the ceiling. Argument 3 is in full force - people have been making up gods for millenia. Only argument 1 can be evaded - is this the Christian god or some other interventionist one who should be leaving fingerprints everywhere, or is it one you made up just for this argument? ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 6, 2010, 7:26am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/105 "2010-03-06T07:26:11Z")
[QUOTE=SteveG1] Wouldn’t it just be easier to admit some things or ideas can not be proved or disproved, and just let it go at that? [/QUOTE] > [@Really\_Not\_All\_That\_Bright](#): > > Of course it would be easier. It would also be easier to let patients in the advanced stages of cancer die; or to reason that some people will die in car accidents no matter what and adding airbags is futile; or to run the hundred meter sprint in 14 seconds instead of 10. > > However, people are willing to put forth the effort in all these cases. None of those are examples of things that can’t be proved or disproved. > [@Really\_Not\_All\_That\_Bright](#): > > There’s nothing in the Bible or Qu’ran that suggests that the Judeo-Christian god is outside the universe. So, god created the heavens and the earth from within his creation and then was somehow constrained by it? Well, that wouldn’t have been very bright. If that is how atheists see the concept, no wonder they can’t buy it. I wouldn’t buy that either. But, it doesn’t seem to me a reasonable view. But, I guess they have to believe that in order to think he must be visible to science. And no wonder they’re perplexed when theists aren’t concerned that science hasn’t been able to pin him down. ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 6, 2010, 7:32am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/106 "2010-03-06T07:32:30Z")
> [@cmosdes](#): > > If you go around and account for everything else in the universe, you have, by elimination, determined there is nothing in the box. And you somewhere have a list of what was in the universe to start with? We cross them off as we come to them, and if we’ve crossed everything off, there’s nothing in the box? ridiculous. ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 6, 2010, 7:43am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/107 "2010-03-06T07:43:37Z")
> [@cmosdes](#): > > The only difference between the empty room and this room is the presence of the box. Since the box raises the probability of the presence of a dead mouse from 0 to non-zero, the box must be providing some evidence that there is a dead mouse in the room. Absolutely not. The presence of the box provides no evidence for the presence of a dead mouse. The box doesn’t “raise” the probability to non-zero. Looking in the empty room drops the probability from non-zero to zero. And to some smaller non-zero value if we see everywhere except in the box. It’s only evidence that changes the probabilities. The drop in probability was based only on the parts of the room we could see and eliminate. And in these cases, probablility is only a matter of our ignorance. There either is or isn’t a mouse in the room, or in the box. When we haven’t looked in the room, we assign a non-zero probability to the possibility of a mouse. If we look, and don’t see a mouse, the self assigned probability drops… to zero if we can see everywhere; eliminate all possibilities; and to some less, but still non-zero value if there is a box. (Or rises to 1 if we see the mouse.) ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 6, 2010, 7:47am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/108 "2010-03-06T07:47:57Z")
> [@cmosdes](#): > > However, the box does provide evidence that there is a dead mouse in there. Every box you haven’t looked in, (and every place you haven’t seen,) is evidence for dead mice? Holy crap, we’re surrounded by the bloody things! I see “evidence” for them everywhere. aaaaaahhhh! Or not. Your view of “evidence” makes no sense. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 6, 2010, 9:12am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/109 "2010-03-06T09:12:27Z")
> [@ch4rl3s](#): > > And you somewhere have a list of what was in the universe to start with? We cross them off as we come to them, and if we’ve crossed everything off, there’s nothing in the box? ridiculous. Never claimed to have a list. I simply stated a truth. If you can eliminate all other possibilities, whatever remains must be the answer. Dark matter and dark energy were born out of this concept. They count up the matter in the universe, see it can’t explain what they observe, and determine there must be things we aren’t yet seeing. [QUOTE=ch4rl3s] Absolutely not. The presence of the box provides no evidence for the presence of a dead mouse. The box doesn’t “raise” the probability to non-zero. [/QUOTE] The box provides for the possibility for the presence of a dead mouse, correct? What do you call something that eliminates some possibilities but allows for other possibilities? I tend to call that evidence for the allowed possibilities. An empty box is allowing for the possibility of a dead mouse. Thus, it is evidence that a dead mouse could be present. [QUOTE=ch4rl3s] Looking in the empty room drops the probability from non-zero to zero. [/QUOTE] Agreed. And since you said the probability drops from non-zero to zero, you must agree the probability of a dead mouse being in the room before you look is non-zero. So what is the difference between a box and a room? What is special about a room that it can have a non-zero probability of a dead mouse but a box can’t? [QUOTE=ch4rl3s] And to some smaller non-zero value if we see everywhere except in the box. It’s only evidence that changes the probabilities. The drop in probability was based only on the parts of the room we could see and eliminate. [/QUOTE] There was some probability that the room contained a dead mouse. Call it P. We look in the room and all we see is a box. The probability that the room contains a dead mouse is now Q which is less than P, and Q \> 0, correct? Why do you assume a non-zero value for P to begin with? And again, what makes the room different than a box? If a room can have a non-zero P, why can’t a box? [QUOTE=ch4rl3s] And in these cases, probablility is only a matter of our ignorance. There either is or isn’t a mouse in the room, or in the box. When we haven’t looked in the room, we assign a non-zero probability to the possibility of a mouse. If we look, and don’t see a mouse, the self assigned probability drops… to zero if we can see everywhere; eliminate all possibilities; and to some less, but still non-zero value if there is a box. (Or rises to 1 if we see the mouse.) [/QUOTE] Probability is always about ignorance. That is the very definition of it. If you know the outcome probability is not involved. But at least you agree that if there is a box the probability that there is a dead mouse in there is non-zero. Given that, your next statement is puzzling. [QUOTE=ch4rl3s] Every box you haven’t looked in, (and every place you haven’t seen,) is evidence for dead mice? Holy crap, we’re surrounded by the bloody things! I see “evidence” for them everywhere. aaaaaahhhh! Or not. Your view of “evidence” makes no sense. [/QUOTE] If you have looked everywhere for a dead mouse and found none, then no dead mouse is around. Wonderful. But if on the other hand a box could contain a dead mouse and you have a box, then you have a slight chance it contains a dead mouse. If you don’t want to call that box evidence, what do you want to call it? Generally speaking, if with a given condition (state, circumstance, whatever) certain things are possible and other things are not, then if that condition exists it is evidence that the things that are possible have occurred. It isn’t by any means proof those things have occurred, just evidence. I fully grant that evidence is generally considered to be something that more than grants the possibility of an event, but rather makes the event _likely_. By that definition, the box is not evidence of a dead mouse. On the other hand, if you add up enough small indicators, pretty soon you have a compelling case and the preponderance of the evidence makes the event likely. Evolution is a good example. Many of the pieces of evidence supporting evolution on their own are not overly strong indicators that evolution is likely, but taken as a group evolution is a certainty. Similarly with a box and a dead mouse. Maybe the box all on its own isn’t “evidence” of a dead mouse, but if you were to put it together with other pieces of information, such as a bad smell or maybe someone witnessing a mouse entering the box but never leaving, you’d consider the box a piece of evidence. It is semantics at that point. Somewhere along the way the box goes from just a box to a piece of evidence. My contention is that the box is evidence regardless of what else you know. The witness testimony is a piece of evidence. The smell is a piece of evidence. The box is piece of evidence. It doesn’t stop being a piece of evidence if we don’t have other other two. ---
**Author:** ![Dan\_Norder](https://avatars.discourse-cdn.com/v4/letter/d/4af34b/32.png) [@Dan\_Norder](https://boards.straightdope.com/u/Dan_Norder)\ **Post date:** [March 6, 2010, 4:29pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/110 "2010-03-06T16:29:48Z")
> [@magellan01](#): > > I can’t believe this nonsense is still being argued. **appleciders** gets it perfectly right in just a few words. I really can’t see how anyone with even a basic understanding of logic cannot grasp this. Unbelievable. > > Wait, maybe this will help: > > Absence of evidence _is_ evidence of absence. It’s not, however, proof of absence. - **appleciders** This bears repeating. I tried a lengthier explanation for the people who weren’t getting it, but if there’s anyone who this thread and \*still \*doesn’t understand they are hopeless. ---
**Author:** ![SteveG1](https://avatars.discourse-cdn.com/v4/letter/s/bb73d2/32.png) [@SteveG1](https://boards.straightdope.com/u/SteveG1)\ **Post date:** [March 6, 2010, 4:39pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/111 "2010-03-06T16:39:43Z")
> [@Dan\_Norder](#): > > This bears repeating. I tried a lengthier explanation for the people who weren’t getting it, but if there’s anyone who this thread and \*still \*doesn’t understand they are hopeless. That’s all well and good, but it still doesn’t sway me, one way or the other. It sounds too much like “if you can’t irrefutably disprove it, it could be true or must be true.” Shouldn’t the main burden of proof be on the person making a claim that something does exist? ---
**Author:** ![Gustav](https://avatars.discourse-cdn.com/v4/letter/g/919ad9/32.png) [@Gustav](https://boards.straightdope.com/u/Gustav)\ **Post date:** [March 6, 2010, 5:07pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/112 "2010-03-06T17:07:28Z")
Seriously, this thread would be maybe 5-10 posts long as most if everyone could just agree that evidence and proof are different things. It’s like two separate conversations are going on parallell to each other, but they think they’re talking about the same thing and respond to each other and it’s just confusing as hell. ---
**Author:** ![SteveG1](https://avatars.discourse-cdn.com/v4/letter/s/bb73d2/32.png) [@SteveG1](https://boards.straightdope.com/u/SteveG1)\ **Post date:** [March 6, 2010, 6:12pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/113 "2010-03-06T18:12:40Z")
> [@Gustav](#): > > Seriously, this thread would be maybe 5-10 posts long as most if everyone could just agree that evidence and proof are different things. It’s like two separate conversations are going on parallell to each other, but they think they’re talking about the same thing and respond to each other and it’s just confusing as hell. OK, so there is a difference between proof and evidence. I still don’t see why, if I read the undertones correctly, a person should agonize over it if all the known evidence points one way, and there is a complete lack of evidence the other way. It seems to be a case where you would first have to suspend disbelief and accept some other argument as a starting point, which also has no evidence, and proceed from there. So, you are starting from a point that is a matter of faith (and not evidence) to begin with. So, I go back to my invisible rhino. The EVIDENCE points to there not being one. I’ve seen no evidence that there is one. So, I can REASONABLY deduce that there PROBABLY isn’t one lurking about. You could apply it to invisible pink unicorns, flying spaghetti monsters, leprechauns, all sorts of things. A lack of evidence may not be proof of absence, but it sure seems to be a strong indicator. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [March 7, 2010, 11:48pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/114 "2010-03-07T23:48:08Z")
> [@cmosdes](#): > > If the probability of a dead mouse goes from 0 to non-zero based on the presence of a box, what do you call the presence of the box? My personally definition of evidence is anything that strengthens a hypothesis should be considered as evidence in favor of that hypothesis. Is that a wrong definition? No, because you are misusing the notion of probability, which is the number of times you expect an event given a certain number of trials. We can only talk about possible and not possible in this case, not probability. > [@](#): > > Given the extraordinarily unlikely event that a random box in a random room has a dead mouse and seeing no other evidence for the presence of mice, I’d quite comfortably assume no dead mouse. In other words, in this case I’d also go with absence of evidence if evidence of absence. I can’t know for sure, but I’m okay with that. In the first case, the mouse was possible, but its presence became not possible due to the lack of evidence of its presence, which would have been expected. In the second case, it was possible that the mouse was either inside the box or outside the box. The lack of evidence expected means that it is impossible for it to be outside the box, but the situation doesn’t change for it being inside the box, no matter what probability you wish to assign to it. ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 8, 2010, 3:23am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/115 "2010-03-08T03:23:16Z")
> [@cmosdes](#): > > Assign the same characteristics to the Flying Spaghetti Monster that you assign to the JC God (outside this world, touches it just once in a while and, not able to be called upon at will, etc.). Now explain what differences there are in the evidence between the two. The only evidence for FSM is people like you who propose its possible existence without actually believing it does. (Unless you want to seriously claim it exists, there is an absense of evidence.) There’s much more evidence for the JCG than that. Starting with the writer who claimed that Israel was set free from Egypt. Continuing with prophets who claimed that Israel prospered when they followed this God, and suffered the natural consequences of their own actions when they didn’t. And through to the witnesses who claim that Jesus died and rose again. And more. There is a lot of evidence. (I’ve never claimed God is scientifically provable. I’ve often said otherwise, so this isn’t scientific evidence.) This is all off topic though. I wouldn’t have even mentioned it, but you seem to think there is as much evidence for FSM as for JCG. That’s just not the case. You are free to reject the evidence as unreliable, but you have to admit that there is much more that you need to ignore for JCG than for FSM. Unless you want to close your eyes, plug your ears and go “la la la la.” But, don’t be suprised when I don’t do the same. ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 8, 2010, 3:30am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/116 "2010-03-08T03:30:31Z")
> [@cmosdes](#): > > If you have looked everywhere for a dead mouse and found none, then no dead mouse is around. Wonderful. But if on the other hand a box could contain a dead mouse and you have a box, then you have a slight chance it contains a dead mouse. If you don’t want to call that box evidence, what do you want to call it? The box is ignorance. > [@](#): > > I fully grant that evidence is generally considered to be something that more than grants the possibility of an event, but rather makes the event _likely_. By that definition, the box is not evidence of a dead mouse. I would have said “more likely,” otherwise that is correct. (and why can’t we leave it at that? sigh) > [@](#): > > On the other hand, if you add up enough small indicators, pretty soon you have a compelling case and the preponderance of the evidence makes the event likely. … Maybe the box all on its own isn’t “evidence” of a dead mouse, but if you were to put it together with other pieces of information, such as a bad smell or maybe someone witnessing a mouse entering the box but never leaving, you’d consider the box a piece of evidence. … My contention is that the box is evidence regardless of what else you know. The witness testimony is a piece of evidence. The smell is a piece of evidence. The box is piece of evidence. It doesn’t stop being a piece of evidence if we don’t have other other two Yes, the preponderance of evidence makes the event likely. But, the evidence is the smell; the evidence is the witness testimony; the evidence is not the box. The box is ignorance. All the box does is prevent us from verifying or eliminating possibilities. It doesn’t change them in any way. Let’s say we have a room you haven’t been in, and your friend says "I have put a dead mouse in that room. And let’s say that’s true. The probability of a mouse in the room is 1. But where? the room is a big “box” to you. complete unknown. The evidence is what your friend did. You step in the room, and it’s no longer a complete unknown, you eliminate possibilities immediately. Everything you eliminate is evidence. Eventually you say, “I have looked everywhere except in the box. So the box must contain the mouse.” The evidence is still not the box, the evidence is everything else you eliminated. (It doesn’t even have to be a box. It can just be a dark corner you didn’t look in. How can a corner you didn’t look in be evidence?) How do I know the box isn’t evidence yet? Because of this possible scenario. Look in the box. In this case, the box is empty. And now, and only now is the box evidence. And what is it evidence of? That you didn’t look everywhere else. Apparently, there was still a dark corner you didn’t look in properly. Let’s try again. Your friend goes into another room and hides the mouse again. This time you thoroughly search everywhere except a shoebox in this room, and we are certain the mouse is in the box. You think, “ha, this time I know the box is evidence.” Really? Ok, so your friend asks you, “did I put a quarter in the box with the mouse? Is there an orange in there? Is there a book? a shoelace? one of a millon other things that could fit in there with the mouse?” Well, are there? Is the box “evidence” for these things? Absolutely not. It’s still ignorance. We are unable to eliminate the possibility. It doesn’t change what the possibility was previously. [QUOTE=Dan Norder] This bears repeating. I tried a lengthier explanation for the people who weren’t getting it, but if there’s anyone who this thread and still doesn’t understand they are hopeless. [/QUOTE] Just to reiterate what I’ve already said previously… Strictly from the definition… “Absence of evidence” can never be “evidence.” if you have “evidence” it can’t be an “absence of evidence.” There is no way around it. If you have something that is evidence of absence, then whatever it is that is indicating absense is by definition evidence. It does seem hopeless based on the number of people who can’t understand that if you have something that can be used as evidence, it is evidence. It isn’t a lack of evidence, even if your evidence is a lack of something else. A lack of expected poo is a lack of poo. and it’s evidence, not a lack of it. it’s a lack of what you expected. If you didn’t expect poo in the first place, the lack of it tells you nothing. You want to know if your neighbour has a new dog. They’ve had one before, and always cleaned up after it. You never saw any poo. You look over the fence now and see no poo. Ah ha!!! That proves it… Oh, right, that proves nothing either way. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 8, 2010, 4:33am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/117 "2010-03-08T04:33:41Z")
> [@Voyager](#): > > No, because you are misusing the notion of probability, which is the number of times you expect an event given a certain number of trials. We can only talk about possible and not possible in this case, not probability. Given 1,000,000 boxes we might find 1 with a dead mouse. I’d call that probability 1 in a million. Each box either has a mouse or doesn’t have a mouse, but that doesn’t mean we can’t assign a probability to each of the boxes. > [@Voyager](#): > > In the first case, the mouse was possible, but its presence became not possible due to the lack of evidence of its presence, which would have been expected. > In the second case, it was possible that the mouse was either inside the box or outside the box. The lack of evidence expected means that it is impossible for it to be outside the box, but the situation doesn’t change for it being inside the box, no matter what probability you wish to assign to it. I’ve lost track. What are the two cases we are talking about? Case 1 is an empty room with no box? And case two is a room with only a box? You seem to be arguing that until we have looked everywhere there is still a possibility there is a dead mouse. And I agree with that. I’ve said that all along. However, if you start with a room the size of Russia and search that entire room, save for one shoebox, and don’t find a single dead mouse, I’d be inclined to believe there isn’t a dead mouse in the room. I don’t need to search every dark corner to be sure. The probability the box contains a dead mouse is the same before and after we searched, but the more we look for something and don’t find it the less likely it exists anywhere. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 8, 2010, 4:48am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/118 "2010-03-08T04:48:30Z")
> [@ch4rl3s](#): > > The only evidence for FSM is people like you who propose its possible existence without actually believing it does. (Unless you want to seriously claim it exists, there is an absense of evidence.) There’s much more evidence for the JCG than that. Starting with the writer who claimed that Israel was set free from Egypt. Continuing with prophets who claimed that Israel prospered when they followed this God, and suffered the natural consequences of their own actions when they didn’t. And through to the witnesses who claim that Jesus died and rose again. And more. There is a lot of evidence. (I’ve never claimed God is scientifically provable. I’ve often said otherwise, so this isn’t scientific evidence.) But you see, you have no evidence about JCG that is any more compelling than evidence for the FSM. That is the entire point of people using the FSM. I know you feel that the “testimony” given in some old book is worth something, but unless that testimony is backed up by something more tangible, you really don’t have anything. Most of any of the verifiable facts in the bible have been shown to be wrong. Eyewitness testimony given 40+ years after the fact is unlikely to be highly accurate. And even today there isn’t one single thing you can point to that is demonstrably a miracle. Show me a re-grown limb and you might have something. You can call all this closing my eyes and plugging my ears, but the point is that your arguments about JCG are as compelling to me as me trying convince you the FSM is real. You can claim JCG is unknowable and beyond scientific reach because you have faith. Great. But you need to understand that to someone who doesn’t have your faith your “evidence” is meaningless and baseless. So, this is back to the OP. In my eye, we’ve looked lots and lots of places to try and find god. Faith healing has been shown to be bunk. Not one person has ever regrown a limb. Bad luck and bad situations seem to be shared equally across all religions and all people. The more we look for god, any god, and don’t find him, the less likely I think it is he exists. Sure, you can keep holding on until you’ve search every rock, nook and cranny, but I’m okay with giving up thinking a coin has a tail side after it has come up heads 1,000,000,000 times in a row. > [@ch4rl3s](#): > > This is all off topic though. I wouldn’t have even mentioned it, but you seem to think there is as much evidence for FSM as for JCG. That’s just not the case. You are free to reject the evidence as unreliable, but you have to admit that there is much more that you need to ignore for JCG than for FSM. Unless you want to close your eyes, plug your ears and go “la la la la.” But, don’t be suprised when I don’t do the same. Please, point me to this evidence of which you speak. If you point me towards the bible I will happily point you towards the old Roman and Greek writings of their gods. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 8, 2010, 5:06am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/119 "2010-03-08T05:06:44Z")
> [@ch4rl3s](#): > > Let’s say we have a room you haven’t been in, and your friend says "I have put a dead mouse in that room. And let’s say that’s true. But we don’t know that is true or not. That is the entire point of this metaphor. We _think_ there is a dead mouse around, but we don’t know one way or another. You can’t pre-suppose the truth. Your friend (or an old text) tells you there is a dead mouse around, and you believe him. > [@ch4rl3s](#): > > You step in the room, and it’s no longer a complete unknown, you eliminate possibilities immediately. Everything you eliminate is evidence. Eventually you say, “I have looked everywhere except in the box. So the box must contain the mouse.” The evidence is still not the box, the evidence is everything else you eliminated. (It doesn’t even have to be a box. It can just be a dark corner you didn’t look in. How can a corner you didn’t look in be evidence?) > > How do I know the box isn’t evidence yet? Because of this possible scenario. Look in the box. In this case, the box is empty. And now, and only now is the box evidence. And what is it evidence of? That you didn’t look everywhere else. Apparently, there was still a dark corner you didn’t look in properly. > > Let’s try again. Your friend goes into another room and hides the mouse again. This time you thoroughly search everywhere except a shoebox in this room, and we are certain the mouse is in the box. You think, “ha, this time I know the box is evidence.” Really? Ok, so your friend asks you, “did I put a quarter in the box with the mouse? Is there an orange in there? Is there a book? a shoelace? one of a millon other things that could fit in there with the mouse?” > > Well, are there? Is the box “evidence” for these things? Absolutely not. It’s still ignorance. We are unable to eliminate the possibility. It doesn’t change what the possibility was previously. Obviously we are talking past one another, so this has become pointless to continue. If you don’t see the box as evidence, that is fair. It was a strained definition of evidence, I grant you. I viewed the box much like you, as ignorance. Your last point seems to be the point _I_ was making. The box could contain lots of things, including a dead mouse. We don’t really know what is in there. But again, if you’ve never seen a dead mouse _anywhere_ (none has ever been shown to exist, only theorized), nor a quarter nor a an orange nor a book nor a shoelace, I’m not about to suspect I’ll find one in the box. There is a chance something like that is in there, but once you’ve looked everywhere _except_ in the box, the chances are exceedingly thin that you’ll find it in the box. The box (ignorance) means we haven’t completely, entirely, without question eliminated all possibilities, but it is close enough to 0 for me. > [@ch4rl3s](#): > > Just to reiterate what I’ve already said previously… Strictly from the definition… “Absence of evidence” can never be “evidence.” if you have “evidence” it can’t be an “absence of evidence.” There is no way around it. If you have something that is evidence of absence, then whatever it is that is indicating absense is by definition evidence. > > It does seem hopeless based on the number of people who can’t understand that if you have something that can be used as evidence, it is evidence. It isn’t a lack of evidence, even if your evidence is a lack of something else. > > A lack of expected poo is a lack of poo. and it’s evidence, not a lack of it. it’s a lack of what you expected. If you didn’t expect poo in the first place, the lack of it tells you nothing. > > You want to know if your neighbour has a new dog. They’ve had one before, and always cleaned up after it. You never saw any poo. You look over the fence now and see no poo. Ah ha!!! That proves it… Oh, right, that proves nothing either way. I agree with all of this, strangely enough. We’ve been arguing the same side the entire time. It really just comes down to how you define “lack of evidence.” You feel looking and not finding is evidence, which I agree with. Others seemed to be arguing that looking and not finding tells you nothing. This is what I thought you meant with the box analogy. ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 8, 2010, 10:04am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/120 "2010-03-08T10:04:27Z")
> [@cmosdes](#): > > But you see, you have no evidence about JCG that is any more compelling than evidence for the FSM. That is the entire point of people using the FSM. I admitted it wasn’t going to be compelling to you. I said there was more of it you had to ignore to believe your point of view. I don’t even have to ignore the evidence to discount the FSM. And that isn’t the point of the FSM. The point is to redefine the debate to be about something, (usually inside the universe,) that’s ludicrous and try to convince someone that it’s still the same debate. It isn’t. Although, some people can be convinced that it is; you were. And as long as you think it is the same debate, you have your eyes closed, your fingers in your ears, going “la la la la,” and you’re trying to convince me to do the same. So, there’s no point me addressing any other point of that post. It’s a hijack of this thread, anyway, and belongs elsewhere. [Previous page](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720.md?page=5) [Next page](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720.md?page=7)