tag:blogger.com,1999:blog-9124539381685751273.post7897290095786242997..comments2023-06-19T04:35:06.263-07:00Comments on Skeptic's Play: Absence of evidence in the Bayesianmillerhttp://www.blogger.com/profile/05990852054891771988noreply@blogger.comBlogger8125tag:blogger.com,1999:blog-9124539381685751273.post-89374904453024954762008-06-09T11:20:00.000-07:002008-06-09T11:20:00.000-07:00Lol, so it's not just me who thinks bigfoot is bor...Lol, so it's not just me who thinks bigfoot is boring! I intended it to be a boring example, so as not to detract from the more general point. SETI is another topic all to itself!<BR/><BR/>As far as SETI is concerned, I don't think it has provided strong evidence that there is no intelligent life out there. Its search space is far too small. However, I think it does suggest that more of the same kind of searching is unlikely to turn up anything.millerhttps://www.blogger.com/profile/05990852054891771988noreply@blogger.comtag:blogger.com,1999:blog-9124539381685751273.post-40901277715550463742008-06-09T08:32:00.000-07:002008-06-09T08:32:00.000-07:00Talking about Bigfoot behind a tree isn't too inte...Talking about Bigfoot behind a tree isn't too interesting an example because people have already looked behind virtually all "trees" on the planet. Each "tree" provided a very, very small evidence of absence, but by the time almost all trees have been looked behind ...<BR/> To me, more interesting real life examples would be the questions of whether their is life on other planets, or intelligent life. Not only is there no convincing evidence that no alien intelligent life has visited earth, but we haven't found radio transmissions yet.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-9124539381685751273.post-81402145098810534832008-06-08T13:59:00.000-07:002008-06-08T13:59:00.000-07:00I already agree with you. I usually take "evidenc...I already agree with you. I usually take "evidence" to mean the probabilistic kind rather than the absolute kind. But if by "evidence" we mean absolute proof, then of course, "absence of evidence is not evidence of absence" is correct.millerhttps://www.blogger.com/profile/05990852054891771988noreply@blogger.comtag:blogger.com,1999:blog-9124539381685751273.post-46127956645419083512008-06-08T11:08:00.000-07:002008-06-08T11:08:00.000-07:00This result and the credo that "absence of evidenc...This result and the credo that "absence of evidence is not evidence of absence" are not contradictory. I see the latter as a statement of logic. Essentially, if A -> B, it does not follow that ~A -> ~B.<BR/><BR/>Bayes theorem deals in probabilistic reasoning which isn't quite the same, as it involves degrees of certainty, not absolutes.<BR/><BR/>To illustrate the difference, imagine you are shown 100 upside-down cups and told that there may be a ball under one or more of them. If you turn over 99 cups and still haven't found a ball, you will probably assign a low probability to the existence of a ball, but you cannot say absolutely that one doesn't exist, because there is still one cup remaining.Alanhttps://www.blogger.com/profile/02129886691899247461noreply@blogger.comtag:blogger.com,1999:blog-9124539381685751273.post-59101666847501500322008-06-06T19:01:00.000-07:002008-06-06T19:01:00.000-07:00When I spoke of bigfoot, I was thinking of a very ...When I spoke of bigfoot, I was thinking of a very mathematically idealized scenario. In reality, we need to consider the possibility of hoaxes and false positives. If multiple independent witnesses see undeniable and self-consistent evidence of bigfoot, that would suffice to overcome most contrary evidence.<BR/><BR/>Or did you mean that different people look in the same place, and only some of them see bigfoot? I'm not sure how that could happen, unless we're talking about pareidolia. Pareidolia is when pattern recognition misfires (ie, seeing <A HREF="http://www.badastronomy.com/bablog/2007/09/21/holy-crepe/" REL="nofollow">Jesus in a crepe</A> or <A HREF="http://www.badastronomy.com/bablog/2008/01/21/speaking-of-dumb-mars-claims/" REL="nofollow">bigfoot on mars</A>).millerhttps://www.blogger.com/profile/05990852054891771988noreply@blogger.comtag:blogger.com,1999:blog-9124539381685751273.post-68224779133543265702008-06-06T12:08:00.000-07:002008-06-06T12:08:00.000-07:00For example, if I found bigfoot behind a tree, tha...<I>For example, if I found bigfoot behind a tree, that would provide extremely good evidence for bigfoot, but if I didn't find him behind a tree, that would provide very weak evidence against bigfoot. But it's still evidence, mathematically speaking.</I><BR/><BR/>ummm... what happens if some of us saw bigfoot behind the tree and some of us didn't?Lindahttps://www.blogger.com/profile/18189439677913352055noreply@blogger.comtag:blogger.com,1999:blog-9124539381685751273.post-57198692908722453792008-06-05T22:46:00.000-07:002008-06-05T22:46:00.000-07:00I think it's a little problematic to simply say th...I think it's a little problematic to simply say that black crows are evidence that swans are white. We need to specify exactly what observation we are talking about. Let's imagine that you see a black thing off in the distance, perhaps a swan, perhaps not. The mere possibility that it is a swan can be evidence against our claim. If we go on to observe that it is a crow rather than a swan, we've acquired evidence for our claim.<BR/><BR/>Of course, all the evidence here is extremely weak. I do not believe in a sharp dichotomy between "weak" and "strong" evidence, but if there were one, this would definitely fall in the weak category!millerhttps://www.blogger.com/profile/05990852054891771988noreply@blogger.comtag:blogger.com,1999:blog-9124539381685751273.post-76154443363250865952008-06-05T10:58:00.000-07:002008-06-05T10:58:00.000-07:00Yay for math!I'm familiar with this notion, but I'...Yay for math!<BR/><BR/>I'm familiar with this notion, but I've sometimes heard it described by example. Say we want to confirm the statement that all swans are white (not actually true, but we'll pretend it is for now). Then seeing a white swan would be evidence of this claim. But seeing a black crow would also be evidence for the claim, since you've seen a non-white thing that turned out to be a non-swan.Anonymousnoreply@blogger.com