# 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:** 5
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [March 2, 2010, 5:29pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/81 "2010-03-02T17:29:10Z")
> [@CurtC](#): > > The question, though, is whether that “nuthin’” can reasonably used to reach any tentative conclusions. I think it can, if it’s a situation where you would expect there to be positive evidence for the thing in question. This is like arguing whether the ends justify the means. Meaningless, unless the situation is clarified. If a satellite is due to enter Earth’s atmosphere in a certain region at a particular time, someone thinks they saw a fiery object streaking across the sky at that time, there’s an impact and a smoking crater, you could reach a reasonable tentative conclusion that the satellite or fragments thereof crashed there, even before recovering identifiable bits of it. If it turns out that it actually was a meterorite, no big deal. On the other hand, if you expect goji berry juice to cure cancer because it’s just chock-full of vitamins and antioxidants and a couple people quoted on a website say their tumors went away after drinking it, that particular absence of evidence has far greater implications, since reaching a “tentative conclusion” that the juice cures cancer would likely cause a lot of people to drink it instead of using proven therapies and dying unnecessarily as a result. So there’s a codicil to **Jackmannii** ’s Law on this subject: Absence of evidence to corroborate extraordinary claims is extraordinarily worthless. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 2, 2010, 5:49pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/82 "2010-03-02T17:49:05Z")
> [@ch4rl3s](#): > > looking at it is evidence alright. It’s evidence of what’s around the box. It’s evidence that the box is a certain size. Those pieces of evidence tell us something. (although we can’t be sure the box isn’t extradimensional, we’re just assuming that based on previous experience.) > > It’s also evidence that nothing came out of the box. However, are you claiming that nothing coming out of the box is evidence for what is or isn’t inside the box? > > So tell me. what more do we know about whats in the box based on what didn’t come out???\* We know it isn’t a planet. We know it isn’t so hot that it will melt the box. We know whatever is in there isn’t so heavy that it will crush through the floor and leave a huge crater behind. We know that whatever is in there must be smaller than the box. We know that whatever is in there isn’t light enough to lift the box off the floor. I’m contending that you can slowly begin to cross off things that can’t possibly be in the box. The more things you can cross off, the less likely it is that _something_ is in the box. If you go around and account for everything else in the universe, you have, by elimination, determined there is nothing in the box. Again, not seeing something come out of the box is evidence that nothing is in the box. > [@ch4rl3s](#): > > > [@cmosdes](#): > > > > As someone else pointed out, this really comes down to how you define “absence of evidence”. If you define that to be looking and not finding anything, then absence of evidence is clearly evidence of absence. > > But looking and not finding anything is clearly gathering evidence. If you look at a box and see nothing come out, we agree you have gathered evidence. What do you think that is evidence of? > [@ch4rl3s](#): > > But, looking here and not finding it doesn’t mean it isn’t over there where you aren’t able to look. Make up your mind. Either you think looking and not finding is evidence or it isn’t. Sure, you haven’t looked everywhere, but the more you look and not find it the more evidence you have it doesn’t exist. I’ll use the same analogy I used with Frank in other threads (and which he completely dodged). Someone flips a coin 1,000,000,000 times and every flip comes up heads. Do you believe you have evidence that the coin doesn’t have a tail? According to you, you haven’t looked everywhere for the tail, so you can’t conclude anything. > [@ch4rl3s](#): > > We have a box. For some reason we can’t look inside it or weigh it. We have one piece of evidence for what is in the box… it’s size. We have an absense of any other evidence. And since you think that absense of evidence is evidence of absense… There must be nothing in the box. Must (proof) and evidence (probability) do not in any way, sense or form mean the same thing. When I look at a box and see nothing come out, I can very comfortably say there is a lower probably that _something_ is in there. Why? Because I’ve eliminated all kinds of things that could have been in there. This is far from certain and I would never conclude there must be something in there just from looking and seeing nothing. On the other hand, if I’ve seen hundreds of boxes that look exactly like this box and not one of them ever had anything in them (I looked at them), then when I look at this one in nearly exactly the same state as all the others and still see nothing coming out of it, I’d very comfortably say there is a high probability nothing is in there. After looking at perhaps thousands of such boxes, I can be pretty sure I’m not going to spend a lot of time on this particular box waiting to see if something comes out. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 2, 2010, 6:49pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/83 "2010-03-02T18:49:50Z")
> [@Jackmannii](#): > > On the other hand, if you expect goji berry juice to cure cancer because it’s just chock-full of vitamins and antioxidants and a couple people quoted on a website say their tumors went away after drinking it, that particular absence of evidence has far greater implications, since reaching a “tentative conclusion” that the juice cures cancer would likely cause a lot of people to drink it instead of using proven therapies and dying unnecessarily as a result How is this in any way absence of evidence? You have evidence, albeit it probably isn’t very good evidence. You can weigh that evidence however you like. When 1,000,000,000 claim it cured them, I might start to think there is something to this. On the other hand, if under scientific scrutiny none of the claims hold, then I’d weigh that, too. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [March 2, 2010, 9:06pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/84 "2010-03-02T21:06:20Z")
> [@cmosdes](#): > > How is this in any way absence of evidence? Anecdotes are not evidence. “My son’s piano teacher’s brother-in-law swears that a drop of this new additive in a tank of gas gives him 300 miles to the gallon!” is not evidence. “In a new report published in _Southwest Indiana Automotive Weekly_, tests made by a part-time refrigerator repairman and a chiropractor on two cabs, a go-kart and a lawnmower showed 20% better fuel efficiency with the new gas additive” is not evidence, at least by commonly accepted standards. “Evidence” in a scientific sense is generally taken as reproducible findings made in one or more well-designed studies conducted with proper controls on a large sample. ---
**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 2, 2010, 9:16pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/85 "2010-03-02T21:16:12Z")
> [@cmosdes](#): > > As someone else pointed out, this really comes down to how you define “absence of evidence”. If you define that to be looking and not finding anything, then absence of evidence is clearly evidence of absence. If, on the other hand, you define “absence of evidence” to mean you’ve never looked, then it does follow that absence of evidence is not evidence of absence. And this falls into my original point. if you don’t look, you don’t expect to see anything, and not seeing anything isn’t evidence of anything. As for the box, it depends on what you are looking for. If you are observing the box to determine if a mouse is in there, as time goes on continued lack of mouse ears popping out or the box shaking or squeaks is evidence of absence of the mouse, since you expect to find them. If you are wondering if a dead mouse is in the box, not so much. ---
**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 2, 2010, 9:30pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/86 "2010-03-02T21:30:15Z")
> [@SteveG1](#): > > I took a “vacation” from this thread for a few. I was having troulbe seeing just what the point of it was. > > I have not seen a rhinoceros on my desk all morning. I didn’t see one last week, or the week before. I have never seen a rhinoceros on my desk. So, I guess, it’s safe to say there never was a rhinoceros on my desk. > > Am I wrong? Must I believe that there may have been one there at some other time that I was not present to observe it? Was it Schroedinger’s Rhino? Do I have to believe in The Great Invisible Rhino Who Magically Doesn’t Crush The Desk? > > Sometimes, just sometimes, there is no evidence of something, simply because it wasn’t ever there. > > I think the OP was saying : > If you can’t disprove it, you have to believe in it. > Wrong Answer. > > Now where’s my cookie? Why don’t you go back and reread the OP? And stop by **magellan01** ’s post while you are at it. To repeat it: Absence of evidence is at best evidence of absence. It is not proof. Thus, your rhino example is pointless, unless you are claiming it is not even evidence that the rhino was not there. Second. when you do not expect to see evidence for a hypothesis, the absence of this evidence is not evidence that the hypothesis is false. If you are hypothesizing primitive aliens around some other star, the lack of radio from them is not evidence they are not there, since you don’t expect to get radio from them. The absence of expected evidence is evidence of absence. Holmes knew that a dog was expected to bark when a stranger entered. The absence of the bark was evidence of the absence of the stranger - and thus pointed to someone else. Elementary. **ch4rl3s** is correct about my pain. 😉 ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 2, 2010, 9:52pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/87 "2010-03-02T21:52:41Z")
> [@Jackmannii](#): > > Anecdotes are not evidence. > > “My son’s piano teacher’s brother-in-law swears that a drop of this new additive in a tank of gas gives him 300 miles to the gallon!” is not evidence. > > “In a new report published in _Southwest Indiana Automotive Weekly_, tests made by a part-time refrigerator repairman and a chiropractor on two cabs, a go-kart and a lawnmower showed 20% better fuel efficiency with the new gas additive” is not evidence, at least by commonly accepted standards. > > “Evidence” in a scientific sense is generally taken as reproducible findings made in one or more well-designed studies conducted with proper controls on a large sample. Anecdotes are evidence. We use eyewitness testimony quite widely for things and how much weight you give that testimony is completely up to you. But it is evidence. I tried to articulate that in my post, although I guess I did it badly. Evidence from structured, reproducible experiments is more convincing than 1,000 pieces of testimony, but that doesn’t make the testimony necessary bad or even useless. How many people had to provide anecdotal evidence that some Toyotas accelerated suddenly before it became believable? ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 2, 2010, 10:05pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/88 "2010-03-02T22:05:13Z")
> [@Voyager](#): > > And this falls into my original point. if you don’t look, you don’t expect to see anything, and not seeing anything isn’t evidence of anything. > > As for the box, it depends on what you are looking for. If you are observing the box to determine if a mouse is in there, as time goes on continued lack of mouse ears popping out or the box shaking or squeaks is evidence of absence of the mouse, since you expect to find them. If you are wondering if a dead mouse is in the box, not so much. I don’t see how looking for something that is impossible to find can possibly be considered having looked for it. By hypothesizing that there is a dead mouse in there that is only detectable by seeing it and then saying that you can’t see it, you’ve set up a non-falsifiable hypothesis. What good is that? **ch4rl3s** is referring to **Frank apisa’s** pain, I think. ---
**Author:** ![SteveG1](https://avatars.discourse-cdn.com/v4/letter/s/bb73d2/32.png) [@SteveG1](https://boards.straightdope.com/u/SteveG1)\ **Post date:** [March 3, 2010, 2:25am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/89 "2010-03-03T02:25:09Z")
> [@begbert2](#): > > Against the “absence of evidence isn’t evidence of absence” that gets whipped out by theistic agnostics, the only real response is “what specifically are you proposing?” If the person is really doing some kind of intellectualist spin cycle with no goal, then one can shrug and admit, “Yeah, there could be an undetectable extraphysical spirit spying on us when we shower - and we could be in the Matrix, or solipsim could be correct, or we could all be characters in a book. What do you expect us to do about it - believe in everything that’s not disprovable, from Sauron to Star Wars? Act on these assumptions? 'Cause if I’m a solipsist there’s no problem if I go around killing people, right?” > > If the person has some kind of agenda, which would be instantly obvious if they do not give solipsism equal time and respect in their arguments, then they can be reasonably dismissed as shills, in my opinion. So then, maybe there is some mysterious invisible rhino, that is sometimes on my desk (according to “them”)? No, I think I’ll continue to believe there never was a rhino on my desk. That makes more sense to me, than playing pointless mind games and useless mental exercises. ---
**Author:** ![SteveG1](https://avatars.discourse-cdn.com/v4/letter/s/bb73d2/32.png) [@SteveG1](https://boards.straightdope.com/u/SteveG1)\ **Post date:** [March 3, 2010, 2:26am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/90 "2010-03-03T02:26:23Z")
> [@CurtC](#): > > Dismissed as _shills_??!? > > Are you suggesting that people are being paid to come to this forum and post things they’d don’t necessarily believe? Can we prove they aren’t? 😃 ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [March 3, 2010, 3:18am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/91 "2010-03-03T03:18:41Z")
Totally depends on the circumstances. The absence of evidence for the Flying Spaghetti Monster is not the same as the absence of evidence for, say, the Judeo-Christian God. People have been looking for evidence of the latter for several thousand years, and finding none; people have never bothered looking for evidence of the former. ---
**Author:** ![SteveG1](https://avatars.discourse-cdn.com/v4/letter/s/bb73d2/32.png) [@SteveG1](https://boards.straightdope.com/u/SteveG1)\ **Post date:** [March 3, 2010, 3:22am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/92 "2010-03-03T03:22:11Z")
> [@Really\_Not\_All\_That\_Bright](#): > > Totally depends on the circumstances. The absence of evidence for the Flying Spaghetti Monster is not the same as the absence of evidence for, say, the Judeo-Christian God. People have been looking for evidence of the latter for several thousand years, and finding none; people have never bothered looking for evidence of the former. 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? ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 4, 2010, 3:00pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/93 "2010-03-04T15:00:45Z")
> [@Really\_Not\_All\_That\_Bright](#): > > Totally depends on the circumstances. The absence of evidence for the Flying Spaghetti Monster is not the same as the absence of evidence for, say, the Judeo-Christian God. People have been looking for evidence of the latter for several thousand years, and finding none; people have never bothered looking for evidence of the former. Two totally different situations. In these cases, we are inside a box and unable to see out. Now, I’m only assuming certain things here, like, the Flying Spaghetti Monster is inside our box, (visible universe,) and more specifically, on this planet. We’ve searched this planet _somewhat_ extensively, and never found it, or Sasquatch, or Nessie. (Though, we do occasionally find a new creature larger than a cat.) I think it is reasonable to say, “the evidence suggests they don’t exist.” The Judeo-Christian God, on the other hand, would be a creature outside the known universe. An able to touch it when and where he wanted, and able to ignore all scientific attempts to force him to show himself. That constitutes an absense of evidence. (By the way, a series of experiments, or rituals, that would require a god to show himself aren’t science… they would be magic.) [QUOTE=cmosdes] ch4rl3s is referring to Frank apisa’s pain, I think. [/QUOTE] I was, but, it will extrapolate. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 5, 2010, 12:31am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/94 "2010-03-05T00:31:23Z")
> [@ch4rl3s](#): > > Two totally different situations. In these cases, we are inside a box and unable to see out. > > Now, I’m only assuming certain things here, like, the Flying Spaghetti Monster is inside our box, (visible universe,) and more specifically, on this planet. We’ve searched this planet _somewhat_ extensively, and never found it, or Sasquatch, or Nessie. (Though, we do occasionally find a new creature larger than a cat.) I think it is reasonable to say, “the evidence suggests they don’t exist.” > > The Judeo-Christian God, on the other hand, would be a creature outside the known universe. An able to touch it when and where he wanted, and able to ignore all scientific attempts to force him to show himself. That constitutes an absense of evidence. > > (By the way, a series of experiments, or rituals, that would require a god to show himself aren’t science… they would be magic.) 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. ---
**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 5, 2010, 1:27am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/95 "2010-03-05T01:27:57Z")
> [@cmosdes](#): > > I don’t see how looking for something that is impossible to find can possibly be considered having looked for it. How do you know it is impossible to find. Though I agree that you don’t really look for the little man who wasn’t there. > [@](#): > > By hypothesizing that there is a dead mouse in there that is only detectable by seeing it and then saying that you can’t see it, you’ve set up a non-falsifiable hypothesis. What good is that? Clearly the presence of absence of the mouse is falsifiable through the experiment of opening the box. (And my box has no lid.) But there are some things we can’t talk about, like what is on the other side of an event horizon. I’m not sure we can generate any useful hypotheses about that. Otherwise, falsifiability include other, plausible experiments and not just the evidence on hand at a given time. For the dead mouse, the evidence at hand at that moment neither supports nor refutes the hypothesis. It is pretty useless, since the expected observation is the same whether or not the hypothesis is true or false. ---
**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 5, 2010, 1:34am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/96 "2010-03-05T01:34:00Z")
> [@ch4rl3s](#): > > Two totally different situations. In these cases, we are inside a box and unable to see out. > > Now, I’m only assuming certain things here, like, the Flying Spaghetti Monster is inside our box, (visible universe,) and more specifically, on this planet. We’ve searched this planet _somewhat_ extensively, and never found it, or Sasquatch, or Nessie. (Though, we do occasionally find a new creature larger than a cat.) I think it is reasonable to say, “the evidence suggests they don’t exist.” > > The Judeo-Christian God, on the other hand, would be a creature outside the known universe. An able to touch it when and where he wanted, and able to ignore all scientific attempts to force him to show himself. That constitutes an absense of evidence. > > (By the way, a series of experiments, or rituals, that would require a god to show himself aren’t science… they would be magic.) I don’t know what the FSM is supposed to do (I’m more of an IPU guy, myself.) But I think the deist god and the Judeo-Christian god are better examples. They both live outside the universe, so they are the same there. The deist god does not interfere with the universe, (after creation) so the lack of evidence for him neither supports nor refutes the hypothesis that he exists. While the Judeo-Christian god also lives outside the universe, the standard model for him has him interacting with us and leaving traces of his presence - the Flood, prophecy, etc. etc. Not finding any of this evidence for his interaction with us is evidence that it didn’t happen. Much of the Bible makes testable predictions - like Jesus coming back. These failing have to have some significance, right? Not proof, clearly, but something. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 5, 2010, 4:20pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/97 "2010-03-05T16:20:13Z")
> [@Voyager](#): > > How do you know it is impossible to find. Though I agree that you don’t really look for the little man who wasn’t there. I’m assuming that by “box” the reference is something we can’t see into. By “dead mouse”, I’m assuming that is a metaphor for something inside the box that will not give any clues it is in there unless you actually look at it. Combing the two, a dead mouse in a box is impossible to find since by definition the only characteristic the mouse has is that it can be seen but the box prevents that from happening. > [@Voyager](#): > > Clearly the presence of absence of the mouse is falsifiable through the experiment of opening the box. (And my box has no lid.) Agree. But again I think the point of the box is that it is something that prevents us from using direct evidence to prove/disprove the hypothesis. > [@Voyager](#): > > But there are some things we can’t talk about, like what is on the other side of an event horizon. I’m not sure we can generate any useful hypotheses about that. Otherwise, falsifiability include other, plausible experiments and not just the evidence on hand at a given time. For the dead mouse, the evidence at hand at that moment neither supports nor refutes the hypothesis. It is pretty useless, since the expected observation is the same whether or not the hypothesis is true or false. This is what I was trying to say with my first point about not being able to see something which is only detectable by seeing it being useless. On the other hand, it might also depend on how you setup the hypothesis. Help me out to see if this makes sense. We can hypothesize that in the room there is a dead mouse. We walk into the room that is completely empty. We can see every bit of space and we see nothing. We’ve shown the hypothesis to be false. If we walk into the same room and see only the box, which is big enough to hold a dead mouse, there is now a non-zero probability that there is a dead mouse in there. 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. My point is this. Whether or not there is a dead mouse is pointless to wonder about since we can never know one way or another and nothing will ever change outside the box if there is a dead mouse in there or not. However, the box does provide evidence that there is a dead mouse in there. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [March 5, 2010, 5:37pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/98 "2010-03-05T17:37:51Z")
> [@cmosdes](#): > > Anecdotes are evidence. We use eyewitness testimony quite widely for things and how much weight you give that testimony is completely up to you. But it is evidence. What might be acceptable in a courtroom and what’s acceptable in the realm of science are two considerably different things. > [@](#): > > Evidence from structured, reproducible experiments is more convincing than 1,000 pieces of testimony, but that doesn’t make the testimony necessary bad or even useless. Anecdotes and personal “testimony” are a potential trigger for research, but they don’t constitute evidence. > [@](#): > > How many people had to provide anecdotal evidence that some Toyotas accelerated suddenly before it became believable? 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. ---
**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 5, 2010, 5:47pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/99 "2010-03-05T17:47:29Z")
> [@cmosdes](#): > > This is what I was trying to say with my first point about not being able to see something which is only detectable by seeing it being useless. On the other hand, it might also depend on how you setup the hypothesis. Help me out to see if this makes sense. Well, that is what this whole thread is about. > [@](#): > > We can hypothesize that in the room there is a dead mouse. We walk into the room that is completely empty. We can see every bit of space and we see nothing. We’ve shown the hypothesis to be false. I’d like to bring it back to evidence, since that is the point here. I agree that the room being empty is evidence of the absence of the mouse. Why? Because the presence of a mouse would imply that the mouse can be seen (in the room under these conditions) and so not finding this evidence is definitely evidence of absence (rising to the level of proof in this case) and falsifies the hypothesis that the mouse exists. > [@](#): > > If we walk into the same room and see only the box, which is big enough to hold a dead mouse, there is now a non-zero probability that there is a dead mouse in there. > > 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. While I’ll agree that the probability of a mouse being in the room is non-zero, we have no idea of what that probability is, and no real way of calculating it. So I’d say that what is going on here is not a probability exercise, but a lack of falsification. When you walk into the room you can have two hypotheses about the mouse - it is in the box, or it is not in the box. You can falsify the not-in-the-box hypothesis as before. You can’t falsify the in the box hypothesis, since the evidence you expect from the mouse being in the box is exactly the same as the evidence you expect from the mouse not being in the box. So you can’t draw any conclusions, other then that you don’t know. > [@](#): > > My point is this. Whether or not there is a dead mouse is pointless to wonder about since we can never know one way or another and nothing will ever change outside the box if there is a dead mouse in there or not. However, the box does provide evidence that there is a dead mouse in there. 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. In your first case, then, the absence of evidence is indeed evidence of absence. 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. Assuming that the mouse hasn’t started to stink, of course.🙂 ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [March 5, 2010, 5:53pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/100 "2010-03-05T17:53:47Z")
> [@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? 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. > [@ch4rl3s](#): > > The Judeo-Christian God, on the other hand, would be a creature outside the known universe. An able to touch it when and where he wanted, and able to ignore all scientific attempts to force him to show himself. That constitutes an absense of evidence. There’s nothing in the Bible or Qu’ran that suggests that the Judeo-Christian god is outside the universe. [Previous page](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720.md?page=4) [Next page](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720.md?page=6)