Precision of this order has been reached by the application of tried and tested Bayesian methodology to model radiocarbon results in the light of other available information (Buck et al. 1996), an approach already employed for Stonehenge (Bayliss et al. 1997). In the case of dates from archaeological contexts, the stratigraphic relationships of the samples are the single more important and most frequently used information.
The steps by which this is achieved are described by Bayliss and Bronk Ramsey (2004) and can be summarised as follows:
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This process can be an extended one, especially as the interval between submitting a sample and receiving the result can be as much as six months.
Sample selection is a crucial step in the process because only samples contemporary with a context will date that context and so be constrained by the relative dating information porvided by stratigraphy. In this project every attempt is made to avoid the dating of redeposited or intrusive samples, by seeking samples which meet the following criteria:
Articulated cattle vertebrae at the base of an outwork ditch on the Stepleton spur of Hambledon Hill
1. Articulated bone, human or animal, excluding burrowing animals
Antler picks at the base of the ditch of the Stepleton enclosure on Hambledon Hill
2. Artefacts with a functional relation to their contexts, such as an antler pick placed on the floor of a newly-dug ditch or a charred post-base from a posthole (provided that the wood is of a short-lived species or that sapwood can be identified)
Burnt material near the base of the ditch of the Shroton spur outwork on Hambledon Hill
3. Multiple single-entity samples of short-life charcoal or charred plant remains from coherent deposits which appear to represent a single event
4. Superficial carbonised residues on the inside of fresh, substantially preserved pots. These are likely to derive from the final contents of the vessel (i.e. recently dead foodstuffs), as distinct from external residues which may include already old material burnt on domestic fires, such as peat or mature wood.
Between 2003 and 2006 this approach was applied to over 400 radiocarbon dates obtained by the project for samples from 35 enclosures, most of them of classic causewayed form, in southern England, as well as in Wales and Ireland. These have been modelled with a similar number of other dates from the enclosures in the context of the gamut of contemporary activity. Stable isotope analysis of human and animal bone samples was also undertaken by Dr Julie Hamilton and Professor Robert Hedges of the Oxford University Research Laboratory for Archaeology and the History of Art.