232
14 New Zealand Palaeodemography
needed to reach a population of 150,000 at the time of Cook (a figure in the interval 125,000–175,000 suggested by the demographer Ian Pool in 1977 [14]). In light
of (iii) and (iv) they suggested the unrealistically high population growth rate of
0.875% p.a., sustained over 919 years, as feasible in the context of the then current
thinking about prehistoric demography in New Zealand. They offered this unsupported increase rate of 0.875% p.a. in place of their own demographically derived
decrease rate of 0.414% p.a..
14.3 Assumptions in Brewis et al.
In this chapter we readdress the issue of the growth rate of prehistoric New
Zealand, employing modern statistical techniques to obtain refinements of the
results obtained by Brewis et al. and in particular to derive confidence intervals
for point estimates of rates of change in order to put analysis on a secure footing.
We begin by examining the assumptions underlying their analysis.
In their analysis Brewis et al. employed a life table approach based on inferences
from skeletal data providing information on ages at death and the total number of
children produced by a woman during her life. The authors utilized the following
assumptions:
(i) except for infants, the distribution of age at death as indicated by skeletal data
represents age-specific mortality rates of the constituent age cohorts;
(ii) the raw proportion (3.5%) of skeletons under age one constitutes an underrepresentation. Two alternative adjustments were proposed: from 3.5 to 15.3%
and from 3.5 to 29.7%;
(iii) a proportion q= 0.488 of births are female;
(iv) each child is born when the mother is 25 years of age;
(v) it is reasonable to base the level of the total fertility of a Maori woman over her
reproductive life on conclusions reached earlier by Phillipps [4].
Assumption (i) was made for convenience of calculation. Citing Sattenspiel and
Harpending [15] and Buikstra et al. [16], Brewis et al. argued that (i) is an approximation because “distributions of age at death generated by osteological analysis are
not necessarily representative of age-specific mortality rates of the constituent age
cohorts”. See also Sutton and Molloy [17].
However, the mode of sampling entailed in obtaining the New Zealand prehistoric skeletal population involves skeletons from a period of some centuries. Other
things being equal, there should be very little, if any, bias in the use of (i) in the
present context. This will be treated in detail in a forthcoming study.
In respect of assumption (ii), Brewis et al. note that the 3.5% infant mortality
indicated by the skeleton population appears unrealistically low. Weiss [18] states
that the healthiest and most successful prehistoric and small-scale populations still
14 New Zealand Palaeodemography
needed to reach a population of 150,000 at the time of Cook (a figure in the interval 125,000–175,000 suggested by the demographer Ian Pool in 1977 [14]). In light
of (iii) and (iv) they suggested the unrealistically high population growth rate of
0.875% p.a., sustained over 919 years, as feasible in the context of the then current
thinking about prehistoric demography in New Zealand. They offered this unsupported increase rate of 0.875% p.a. in place of their own demographically derived
decrease rate of 0.414% p.a..
14.3 Assumptions in Brewis et al.
In this chapter we readdress the issue of the growth rate of prehistoric New
Zealand, employing modern statistical techniques to obtain refinements of the
results obtained by Brewis et al. and in particular to derive confidence intervals
for point estimates of rates of change in order to put analysis on a secure footing.
We begin by examining the assumptions underlying their analysis.
In their analysis Brewis et al. employed a life table approach based on inferences
from skeletal data providing information on ages at death and the total number of
children produced by a woman during her life. The authors utilized the following
assumptions:
(i) except for infants, the distribution of age at death as indicated by skeletal data
represents age-specific mortality rates of the constituent age cohorts;
(ii) the raw proportion (3.5%) of skeletons under age one constitutes an underrepresentation. Two alternative adjustments were proposed: from 3.5 to 15.3%
and from 3.5 to 29.7%;
(iii) a proportion q= 0.488 of births are female;
(iv) each child is born when the mother is 25 years of age;
(v) it is reasonable to base the level of the total fertility of a Maori woman over her
reproductive life on conclusions reached earlier by Phillipps [4].
Assumption (i) was made for convenience of calculation. Citing Sattenspiel and
Harpending [15] and Buikstra et al. [16], Brewis et al. argued that (i) is an approximation because “distributions of age at death generated by osteological analysis are
not necessarily representative of age-specific mortality rates of the constituent age
cohorts”. See also Sutton and Molloy [17].
However, the mode of sampling entailed in obtaining the New Zealand prehistoric skeletal population involves skeletons from a period of some centuries. Other
things being equal, there should be very little, if any, bias in the use of (i) in the
present context. This will be treated in detail in a forthcoming study.
In respect of assumption (ii), Brewis et al. note that the 3.5% infant mortality
indicated by the skeleton population appears unrealistically low. Weiss [18] states
that the healthiest and most successful prehistoric and small-scale populations still