occurrence of secondary dispersal centres (see for
example Hodder and Orton 1976). These phenomena may be recognisable in
simple point-distribution maps wherein the presence or absence of the
artefacts under discussion is plotted (e.g. the distribution of Colchester
mortaria - Hartley 1973a, fig. 7), but the facility of discussing
relative quantities of artefacts enables a greater depth of discussion of
such phenomena to take place.
Four measures of quantity were considered by Orton (1975; cf.
1980, 156—67) in a paper aimed at assessing the merits and demerits of
each measure. Two criteria for assessment were proposed: (i) the measure
should give a ‘good’ estimate of the relative proportions of different
types
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in one context, and more importantly (ii) it should be such that valid
comparisons of these proportions can be made between one context and another’.
The four measures are subsequently ordered in decreasing merit: equivalent
number of vessels; weight of sherds; number of sherds; number of vessels
represented (often expressed as a minimum). The present author consequently
elected to employ the first method; rim sherds only were analysed, as these
provide information about the form, size and function of vessels that is
rarely discernible from base sherds, which tend to exhibit a high degree of
formal conservatism and less variety in size than rims. The method has the
incidental advantage that only a small proportion of an
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