Biology Reference
In-Depth Information
FIGURE 11.2 Normal
densities for male and for
female femoral circumfer-
ences (as in Figure 11.1),
but with nine females to
every one male. Note how
this uneven sex ratio shifts
the sectioning point up to
60.2 mm from the previous
value of 57 mm.
F
M
40
50
60
70
Femoral Circumference (mm)
and “hessian” we find an estimated proportion of males of 0.1005 with a standard error
of 0.0114. As with our previous example from the brow, we can now use Bayes'
theorem to find the probability that an individual with a given measurement is male
(or female):
ffx; 63; 4:1g0:
1 00 5
PðMjxÞ¼
:
(11.11)
ffx; 63; 4:1g0:
1 00 5 þ ffx; 51; 4:2gð1 0:1005Þ
For a measurement of 60.2 mm (which we saw was our correct sectioning point) the proba-
bility that the individual was a male is 0.4996, or essentially 0.5. This is the 50:50 that we
would expect for someone at the proper sectioning point. In contrast, for a measurement
of 57 mm (our original sectioning point) the probability that the individual was a male is
0.0981. Again, if this were the correct sectioning point the probability that an individual
was male at this measurement should be 0.5.
ESTIMATI ON OF AGE AND OF THE AGE-AT-DEATH ST RUCTURE
In the past, analysis of the age-at-death structure in skeletal samples rested on the
construction of life tables from counts of individuals (or deaths) within particular age indi-
cator states. Then in the 1980s and 1990s, scholars began cross-tabulating one or more age
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