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Bayesian thinking – and trusting one’s gut



/Laszlo Bencze

In “Does trusting your gut make you unscientific?” (New Scientist, 13 April 2012), astrophysics postdoc Andrew Pontzen reflects,

I’ve been popping up at a few science festivals recently, discussing the evidence for dark matter with particle physicist Tom Whyntie. After a session at Cambridge Science Festival, UK, a man in a duffle coat approached me to explain that Einstein was wrong – that the universe is not, in fact, expanding. (Actually, a static universe would have pleased Einstein greatly, but that’s beside the point.) As evidence, he tried to give me his book on reinterpreting the redshift of galaxies. When I politely refused, he accused me of being “unscientific”.

The implication is that being “scientific” means completely digesting and testing every idea before deciding whether it’s right or wrong. But sometimes we have to make fast decisions based on prejudice, or we’ll never get anything done. Is that OK, or does it fundamentally undermine what we’re trying to achieve?

He offers some thoughts on Bayesianism as it relates to the faster-than-light neutrinos (which weren’t).

Most scientists are wise to trust their gut at least some of the time. Here’s another example, one that should happen more often. The scientist reads a journal article claiming findings that are just exactly what popular opinion might expect. (Or, on some subjects perhaps, just exactly what elite opinion might expect.) And it keeps happening again and again. No challenges, no surprises. No pesky bits of contrarian data.

Yes, that’s right, I am thinking of Diedrik Stapel, the disgraced Dutch researcher whose social psychology research confirmed a good many prejudices within his discipline. Other researchers at first accepted what he had made up for precisely that reason. And he wasn’t alone.

I don’t know if Bayesianism can help here; sometimes what is needed is intuition, the kind that comes with experience: If data is picture perfect, maybe that’s what it is, a picture. And a frame.

Curiously, there’s an application for this approach in the arts as well. Recently, a number of autobiographies on the market have turned out to be fictional. A red flag is that they are not only fictional but stereotypical. Full of characters you would meet in a sociologist’s textbook or an activist’s bid for media coverage. Or in soap operas. Or anywhere but on the street.

Sensitive critics began to get suspicious, in many cases. That’s intuition at work. The moment one finds oneself asking, “Could this really be true?” is not usually the moment one has the evidence that it isn’t. It’s the moment when one should feel free to articulate one’s doubts, at least to oneself. Work with the doubts until they can be expressed in a logical and rational manner.

Doubts that can be clearly framed can be researched. That’s where the orthodox methods of science (or investigation in general) are essential. But many doubts must begin as intuitions that something is wrong; there isn’t really any other way to go about it.

If that feels too subjective for some people, they had best prepare themselves to be hoaxed a lot.

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The discussion in the blogpost highlighted, was about Bayesian reasoning used to evaluate evidence. The author argues that we hold scientific theses with varying degrees of confidence, and data we use to reverse these theses is likewise of varying levels of confidence. Carl Sagan famously intoned "Extraordinary claims require extraordinary evidence", which is a summary of this Bayesian claim. Unfortunately, when his competitor on the NASA Viking lander discovered life while Sagan's multi-million dollar instrument didn't, he could pull out this bromide to dismiss his competitor's discovery. You know how that works, "My data is extraordinary, yours is simply ordinary." Which is why we have Thomas Kuhn telling us that these Bayesian priors are inextricably linked to sociological categories. Whatever the crowd thinks is extraordinary, is what you think too. But this is all so very subjective. Germany accepted plate tectonics in geology decades before it was "acceptable" in America--an elderly geophysicist once explained to me in a delightful German accent. Some communities are more progressive than others, does this mean that all science is relative to the community? Certainly the Post-moderns think so. Some frightening email exchanges from defenders of "Anthropogenic Global Warming" demonstrate that the facts should not get in the way of a dominant community theory. Wasn't that what Nietzsche said about the Superman? Surely there must me something true that isn't just in our head. Surely there must be a reality that is the same for everyone. Surely there must be regular laws of nature that remain true for all generations. Surely there must be reasoning which is infallible for all time. And what if the man in the duffel coat was carrying around a sheaf of papers that had that reasoning in it? Would it matter if it contradicted the combined intellect of the world's cosmologists? And how would we know? That is the real question, and the one my post-modern blogger never answered. Robert Sheldon

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