Wednesday, March 11, 2009

Proof and Probability

NOTE: The image in question is now know to be a forgery.

This is expanded from a comment I left on Cyberthrush's blog.

There is a fundamental reason why, in all likelihood, it will never be possible to absolutely rule out a Pileated Woodpecker in the case of Steve Sheridan's 2007 Mystery Woodpecker Photo. The white shield may be very unlikely, the appearance of the neck may be just as unlikely, but you have to consider the phenonenon of preselection. This image has been singled out from an untold number of other shots of large crested woodpeckers, accidental and intentional, precisely because of this unlikely confluence. It is not a random selection. So, even if we were to conclude that each of those events had, say, a 1:1000 chance, so the combination has a 1:1,000,000 chance... but there might have been 1000 or even 10,000 images of Pileateds taken over the last several decades by people knowledgeable enough to single this out. We really have no idea of that number. Even if it is as low as 1000 shots, our odds are down to 1:1000 for this bird; if it is 10,000 shots we're down to 1:100 odds on this bird. In reality we don't know anything about these various numbers other than that they are all pretty large. If the photo showed a visible dorsal stripe, then the triple coincidence would become so much more unlikely that even the preselection effect would be overcome in the judgement of most reasonable reviewers, I suspect. This is especially true when you consider that it is much easier to imagine leucism creating a large patch of white flight feathers than a narrow strip of white mantle feathers. But we don't have a visible dorsal stripe, so I don't really think there is any way anyone will ever push this bird past the barrier for being identified conclusively as an Ivorybill. It is still intriguing discovering how close it might get to that wall! And, in that gap between likelihood and scientific certainty is where the realm of personal beliefs, feelings, and opinions is found. Thus we have, and will probably have more, people who personally feel this bird is an Ivorybill, and get a thrill from that, but will also state that scientifically they feel that a very odd Pileated photo can not be conclusively ruled out.

And there is nothing unscientific about that.


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