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Types of Chronological Information
The types of information which can be used to make chronological
inferences can be divided into two broad categories: the first
are the age measurements themselves and the second are the
stratigraphic relationships (see Harris)
between samples.
Our knowledge about the actual age of archaeological artifacts
can come from a variety of sources:
All of these different types of information can be introduced into an
archaeological model built with OxCal.
See also [Program Operation]
Some artifacts such as coins can be directly dated by using
information from the historical record.
Such information can usually be written in terms of a specific
year (C_Date) perhaps with an error
term associated with it (given in this program as one standard
deviation).
See also [Program Operation]
[Example]
[Mathematical Methods]
Radiocarbon dates must be calibrated in order to use them in
conjunction with other techniques or if any chronological inferences
(such as the length of phases) are to be
made(see Bowman 1990 or
Aitken 1990).
These are entered in this program as radiocarbon dates
(R_Date) with an error quoted
as one standard deviation (the form used by all radiocarbon
laboratories). It is assumed that any laboratory multiplier has
already been applied.
See also [Program Operation]
[Example]
[Mathematical Methods]
The methods of thermo-luminescence (TL) and optically stimulated
luminescence (OSL) dating are particularly important beyond the
range of radiocarbon or in the many sites where preservation of
organic material is poor.
Both methods are a measure of accumulated radioactive dose from a site
since the samples were subjected to heat (TL) or sunlight (OSL).
The raw results can be entered into this program by defining the year
of measurement (Year) the site dose
rate (Dose) and associated error
(Error) and then entering the
measured doses received by the samples which yield a calendar age
(L_Date).
Alternatively since the laboratories will frequently give the results
in the form of calendar ages they can simply be entered in the same
way as historical information.
One feature of luminescence dates is that they sometimes have
asymmetric errors associated with them these can also be entered by
either method.
See also [Program Operation]
[Mathematical Methods]
Information from other dating methods such as dendro-chronology
or Uranium series can usually be entered in the form of calendar
dates (C_Date) possibly with
asymmetric errors.
There may also be other forms of information which you wish to include
in a study.
Many of these it will be possible to write in the form of calendar
ages in conjunction with `stratigraphic' information.
It is also possible with this program to define your own probability
distributions and use them in the analysis
(Prior).
Because of the variable nature of the radiocarbon calibration curve
it is often
difficult to predict beforehand how good a set of radiocarbon dates
are likely to be in answering a set of archaeological questions.
This program incorporates a technique
(R_Simulate) for generating a
radiocarbon
date (with random but realistic errors) given the calendar age
expected and the error term that the radiocarbon lab is capable
of providing.
Using this it is possible for the archaeologist to try out different
possible dating programs and see how much information he is likely
to be able to gain from them.
See also [Program Operation]
[Example]