Lewis on radiocarbon
Apr 17, 2014
Bishop Hill in Climate: Statistics

Nic Lewis has a very long and rather technical post up at Climate Audit about the Bronk Ramsey radiocarbon dating algorithm and its statistical problems. It's well worth perservering with though, because when he gets on to testing different statistical approaches to the problem - the Bronk Ramsey subjective Bayesian one, an objective Bayesian one, and a frequentist approach too - the failings of the subjective Bayesian approach become startingly clear.

The different approaches are also considered by means of a rather fascinating analogy, namely the recovery of a satellite that has fallen to Earth.

This is the conclusion of Nic's paper:

...there seems to me no doubt that, whatever the most accurate method available is, Doug is right about a subjective Bayesian method using a uniform prior being problematical. By problematical, I mean that calibration ranges from OxCal, Calib and similar calibration software will be inaccurate, to an extent varying from case to case. Does that mean Bronk Ramsey is guilty of research misconduct? As I said initially, certainly not in my view. Subjective Bayesian methods are widely used and are regarded by many intelligent people, including statistically trained ones, as being theoretically justified. I think views on that will eventually change, and the shortcomings and limits of validity of subjective Bayesian methods will become recognised. We shall see. There are deep philosophical differences involved as to how to interpret probability. Subjective Bayesian posterior probability represents a personal degree of belief. Objective Bayesian posterior probability could be seen as, ideally, reflecting what the evidence obtained implies. It could be a long time before agreement is reached – there aren’t many areas of mathematics where the foundations and philosophical interpretation of the subject matter are still being argued over after a quarter of a millennium!

I gather that the story still has a way to run, so watch this space.

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