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Subject:

Controversy over radio carbon dates

From:

Michael <[log in to unmask]>

Reply-To:

British archaeology discussion list <[log in to unmask]>

Date:

Wed, 26 Nov 2014 11:50:34 +0000

Content-Type:

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On a blog I read on climate a serious archaeological controversy over 
carbon dating is being aired. Unfortunately, much of it is 
undecipherable even though I have a science degree, but it seems C14 
dating is so key that it is important enough that archaeologists should 
be aware. So I will outline what I can decipher as best I am able.

As far as I can see the core of the issue is how probabilities derived 
from carbon dates are combined to derive an estimate of the actual date. 
And to avoid alarm, it appears to amount to whether the method used is 
the mathematically best way to do this, not whether the dates are 
grossly wrong.

To give a flavour of the issue an example is used with three calendar 
dates (9AD,10AD,11AD) which because of variation in C14 levels, two show 
with the same C14 date 9AD->110, 10&11AD->100). Then it suggests that 
when the probability of each of the two C14 dates (110 & 100) are the 
same then there is a 50% chance of the date being 9AD. Instead it seems 
to be suggested that OxCal gives a 33% probability.

I'm not sure how it got to this, but Doug Keenan has accused Christopher 
Ramsey of fraud and has issued a formal complaint to the University of 
Oxford. However, during the discussions on the original blog post at 
Bishop HIll discussing the issue (which I missed), serious doubts were 
raised with part of what Keenan was saying:

    Nic Lewis: "In my view Ramsey's method doesn't represent best
    scientific inference either. However, the issues are complex and,
    predicated on his assumed uniform prior in true calendar year,
    Ramsey seems to have followed a perfectly defensible approach. So I
    don't see it can be a matter of misconduct – rather it is an issue
    of poor program documentation, including key assumptions only being
    set out in referenced papers (and not necessarily being justified).
    The statistical issues involved certainly merit further debate. " (
    http://bishophill.squarespace.com/blog/2014/3/30/dating-error.html)
    <http://bishophill.squarespace.com/blog/2014/3/30/dating-error.html>

But this still leaves a concern over carbon dates. Now from the latest 
blog post 
(http://www.bishop-hill.net/blog/2014/11/26/the-pursuit-of-ramsey.html) 
it appears Keenan is intending to take this further:

    *Keenan*: "I asked the police to investigate Ramsey for misconduct
    in public office. The police declined to investigate. I decided to
    obtain legal advice on that question. Additionally, I decided that
    if the advice was positive, I would not report the matter to the
    police; instead, I would undertake a private prosecution."
    But this has not been the end of the affair. Doug has rewritten the
    complaint, bringing in a new allegation that he had held back
    previously and has put the whole thing to the University.


*Summary of original issues:**
*
Ramsey is the author of a computer program that implements the 
calibration procedure. The program, OxCal 
<https://c14.arch.ox.ac.uk/embed.php?File=oxcal.html>, is very widely 
used by radiocarbon scientists, and has been for decades. Keenans 
accusation appear to be:

1. An error in the calibration procedure for translating from C14 to 
calendar date as per example above (but see Nic Lewis comment above)

2. The use of a method that is appropriate for different samples for 
repeated measurements on a single sample

Mike

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