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Assessment of race from the pelvis.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 62205-208 (1983)
Assessment of Race From the Pelvis
M. YASAR ISCAN
Department of Anthropology, Florida Atlantic Uniuersity, Boca Raton,
Florida 33431
KEY WORDS Racial assessment, Discriminant function analysis,
Pelves, American whites, American blacks
ABSTRACT
Racial assessment of human postcranial skeletal remains has
been a major concern for forensic and skeletal anthropologists. Materials (N =
400) of the present study are from the Terry Collection and consist of 100 black
and white American pelves of both sex with known age and race. Measurements were taken from the articulated pelves. Results of discriminant function
analysis indicate classificatory accuracy may be a s high as 88%. Transverse
pelvic breadth contributes more to the function than biiliac breadth and antero-posterior height. The females are more easily assessed racially than males.
Although a highly reliable classification is produced, the results of the study
should be employed with caution, a s samples were of questionable nutritional
status and of low socioeconomic class.
The femur is the most studied bone of the
postcranial skeleton in the assessment of the
biological affinity of a n individual (Stewart,
1962; Gilbert, 1976; Walensky, 1965).Obstetrically oriented radiographical investigations have shown that there are metrical differences, especially in the dimensions of the
pelvic inlet, among human populations
(Scheyer, 1934; Aiman, 1976; Torpin, 1951).
However, a study by Todd (1929) on a cadavera1 population pointed out that the differences between American blacks and whites
are small, admitting that this part of the
skeleton has not been "entrenched" adequately. A later comparative osteological
work reemphasized that pelves of the white
population are larger than those of American
Indians and blacks (Howells and Hotelling,
1936). The human pelvis has played a minor
role in assessing the biological affiliation of
skeletal remains found in archaeological and
forensic sites (Bass, 1969,1979; Kerley, 1978;
Krogman, 1962; Stewart, 1979). The present
paper is a n attempt to develop a simple statistical technique to determine the racial difference between American blacks and whites,
using pelvic measurements.
MATERIALS AND METHODS
Four hundred pelves (100 each sex-race
group) of American blacks and whites were
c,(
1983 ALAN R LISS. INC
utilized as the main sample in this study.
The age, sex, and race of all specimens in the
sample were known. They are a part of the
Terry Collection at the Smithsonian Institution of American skeletal material from the
19th and early 20th centuries.
Before any measurements were made, the
pelves were articulated with several rubber
bands while leaving a small gap between the
pubic bones, a procedure used by Howells
and Hotelling (1936). Three measurements
were selected by a stepwise discriminant
function procedure from the original 12 dimensions and then incorporated into the
analyses. The biiliac breadth was measured
by a n osteometric board as the maximum
distance between the iliac crests. The antere
posterior height, also known as conjugate diameter, was taken from the sacral promontory to the pubic crests of both sides and the
average of the two was recorded. The transverse breadth was obtained as the maximum
distance between the arcuate lines of the pelvic inlet. A sliding caliper was used for these
two dimensions.
The main sample of the study was randomly divided into base (N = 75 for each sex
and race) and test (N = 25 for each sex and
race) samples. The base sample was used to
Received September 28, 1981;accepted May 26, 1983
206
M.Y.
CAN
compute both descriptive and t-test statistics.
The base samples of the same sex of both
groups were utilized to develop several canonical discriminant function statistical
models. The statistical analyses were carried
out according to the latest version (version 8)
of the Statistical Package for the Social Sciences subroutines (Nie et al., 1975; Hull and
Nie, 1979). Discriminant scores of the test
samples were calculated according to the unstandardized canonical discriminant function coefficients obtained from the base
sample. In all these calculations the males of
both races were treated separately from the
females.
blacks.
The relative accuracy of a correct classification is shown in Table 3. In the base sample, the highest classification accuracy is
88%. In the function where age is not included this rate drops to 79% in males and
83% in females. Overall, females seem to
show better predictive results than males.
Classification results of the test sample correspond well with those of the base sample
(Table 3). However, males of the test sample
are predicted slightly higher than the
females.
DISCUSSION
Race determination from the cranium has
provided successful results. Howells (1970)
RESULTS
was able to classify a skull into a race with a
As Table 1 illustrates, it is evident that in 90% accuracy. Giles and Elliot (1962) showed
all variables whites of both sexes exceeded a slightly lower percentage in their analysis
blacks of the corresponding sex, with a statis- of American blacks and whites. The present
tically significant difference between the study reached a n accuracy of 83% in males
means. The F-ratio statistic in the same table and 88% in females. Such a result, although
signifies that in all dimensions the sample less successful than those based on cranial
variances are the same. The age variance of measurements, is promising for various reasons. First, the pelvic area has not been used
sample females is, however, heterogenous.
The results of the canonical discriminant in race determination; second, the number of
coefficients are presented in Table 2. The measurements involved were minimal; and
standardized coefficient represents the rela- third, these measurements could be taken
tive contribution of a variable to the func- with minimal interobserver errors.
This study also showed that, of the three
tion. It is clear that in multivariable
functions the antero-posterior is the factor dimensions, transverse and biiliac breadths
that contributes least while the transverse seem to be homogeneously distributed within
breadth is the most powerful of the four var- a race. However, the antero-posterior height
iables. The influence of age is undeniably is more varied. In previous studies such obhigh. The unstandardized coefficient is the servations were also noted. Research in obweighting coefficient to be used in calculat- stetrical disciplines has indicated that the
ing the discriminant score for a given pelvis. antero-posterior height is a sensitive dimenThe positive values, i.e., larger than zero, sion of the human skeletal architecture and
signify a n association with the white sample responds to environmental and socioeconompopulation. The reverse score is for the ical factors of the population. A major reTABLE I . Means, standard deuiations, and F and t statistics IN
Variables'
Male
Age (in years)
Biiliac breadth
Transverse breadth
Antero-posterior height
Female
Age (in years)
Biiliac breadth
Transverse breadth
Antero-posterior height
White
Mean
SD
Black
Mean
SD
58.52
273.96
123.59
108.73
13.07
16.10
7.95
9.62
49.36
254.60
111.96
102.01
65.24
277.99
133.93
116.64
15.94
17.11
8.09
10.51
47.88
252.81
120.56
110.75
'All dimensions in millimeters.
'All t's in both races significant a t P < 0.001
,'Significant at P < 0.026 (two-tailed test).
=
75 each sex-race)
F
tL
15.40
15.27
7.39
8.54
1.39
1.11
1.16
1.27
3.93
7.55
9.28
4.53
20.70
15.95
6.82
9.26
1.6g3
1.15
1.40
1.29
5.75
9.32
10.95
3.64
207
ASSESSMENT OF RACE FROM THE PELVIS
T A B L E 2. Canonical discriminant function coefficients
Functions and
variables
Standardized
coefficients
1)Biiliac breadth
1.000
Constant
2) Transverse breadth
Constant
3) Biiliac breadth
Age
Constant
4) Transverse breadth
Age
Constant
5) Biiliac breadth
Transverse breadth
Constant
6) Biiliac breadth
Transverse breadth
Age
Constant
7) Transverse breadth
Antero-posterior height
Age
Constant
8) Biiliac breadth
Transverse breadth
Antero-posterior height
Constant
9) Biiliac breadth
Transverse breadth
Antero-posterior height
Age
Constant
Males
Unstandardized'
coefficients
Females
Unstandardized'
coefficients
.ooo
0.0637219
0.0604552
-16,04480
0.1336859
- 17.01109
0.0510116
0.0196656
- 14.65077
0.1181089
0.0244722
-16.41311
0.0175062
0.1036824
- 17.83939
0.0033984
0.1127945
0.0237207
- 16.59630
0.1 116498
0.0172727
0.0252114
- 17.59680
0.0169375
0.1004562
0.0117874
- 18.61806
0.0019737
0.1086451
0.0170556
0.0247657
-17.68839
1
- 16.84043
1.000
Standardized
coefficients
0.1303004
1.000
- 15.34591
0.891
0.293
0.0567736
0.0205256
- 16.11140
0.1199950
0.0273070
-- 15.60514
0.0179339
0.1035484
-16.93482
0.921
0.390
0.281
0.795
0.844
0.363
0.883
0.452
0.290
0.776
0.122
0.839
0.361
0.056
0.844
0.438
- 16.27929
0.1003125
0.0425694
0.0337675
-18.12124
0.0147927
0.0975458
0.0253182
- 18.06558
- 0.00107 13
0.1016162
0.0429505
0.0341109
- 18.05033
0.770
0.387
0.483
0.232
0.745
0.230
-0.017
0.780
0.391
0.487
0.835
0.171
0.466
0.280
0.751
0.117
0.032
0.813
0.169
0.458
'Discriminant score less t h a n 0 would classify as black.
T A B L E 3. Correct prediction percentage of base and test samples
Function
White
Base
Black
76.0
74.7
80.0
76.0
73.3
80.0
81.3
74.7
82.7
74.7
77.3
78.7
85.3
84.0
85.3
82.7
80.0
82.7
76.0
78.7
81.3
88.0
80.0
86.7
88.0
80.0
88.0
78.7
88.0
76.0
88.0
85.3
86.7
88.0
86.7
88.0
White
Test
Black
75.3
76.0
79.3
80.7
78.7
82.7
82.0
77.3
82.7
88.0
80.0
84.0
88.0
80.0
92.0
88.0
88.0
88.0
76.0
84.0
76.0
84.0
80.0
92.0
88.0
88.0
88.0
82.0
82.0
80.0
86.0
80.0
92.0
88.0
88.0
88.0
77.3
83.3
78.7
88.0
82.7
86.7
88.0
83.3
88.0
72.0
60.0
84.0
84.0
72.0
84.0
84.0
76.0
80.0
76.0
88.0
88.0
88.0
84.0
84.0
88.0
88.0
88.0
74.0
74.0
86.0
86.0
78.0
84.0
86.0
82.0
84.0
Average
Average
Males
1)
2)
3)
4)
5)
6)
7)
8)
9)
Females
1)
2)
3)
4)
5)
6)
7)
8)
9)
M.Y. ISCAN
208
sponse of this diameter is a reduction in
height in individuals living under nutritionally and socioeconomical disadvantaged conditions (Nicholson, l945; Caldwell et al.,
1934; Thoms, 1936). It has also been implied
that such a decrease in antero-posterior
height is due to reorganization of the sacroiliac joint resulting from the weight and child
bearing functions of the pelvic girdle (Derry,
1923; Caldwell et al., 1934; Igcan, 1980). From
this it can be concluded that transverse and
biiliac diameters should be of value for determining race differences between populations
since environmental impact is relatively less
on these variables than on the antero-posterior diameter.
There are the usual limitations in using
discriminant function studies. These limitations include the representativeness of the
sample, so that the result can be used on a
racially similar population. This issue was
raised by Birkby (1966) in regard to the study
by Giles and Elliot (1962). A second issue is
the change in a population through time.
Angel (1976) pointed out that there is a secular change in pelvic dimensions since human prehistory. The occurrence of such a
change is also supported by Igcan (1980) in
his earlier study of the Terry Collection in
which it was shown that, among other measurements, antero-posterior height in recent
populations has become larger. One should
then be cautious in applying the result of the
present study to a prehistoric or a more recent population. The final issue deserving
mention here is that the age variable plays
an important role in the discriminant function, and exact age may be the most difficult
factor to determine.
In conclusion, this study is a n attempt to
fulfill a need (Stewart, 1973) that is necessary for determining racial affinity from the
postcranial skeletal remains. It should serve
skeletal and forensic anthropologists in their
analysis of remains found under commingled
conditions as well as in a situation where
cranially determined race identification may
require support from the postcranial remains. Modern samples, however, should be
tested before reaching a statistical decision
based on the results of this study.
ACKNOWLEDGMENTS
This research was supported in part by the
Smithsonian Institution (Ales HrdliEka
Fund). The author is grateful to Dr. Walda
Igcan for commenting on the manuscript.
Many thanks to Mrs. Marjorie Wolf for her
excellent typing.
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Angel, JL (1976) Colonial to modern skeletal change in
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Bass, WM (1969) Recent developments in the identification of human skeletal material. Am. J. Phys. Anthropol. 30t459-461.
Bass, WM (1979) Developments in the identification of
human skeletal material (1968-1978). Am. J. Phys.
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Caldwell, WE, Moloy, HC, and D’Esopo, DA (1934) Further studies on the pelvic architecture. Am. J. Obstet.
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