Determination of sex from skeletal remains is performed using a number of methods developed by biological anthropology. They must be evaluated for consistency and for their performance in a forensic setting. Twenty skeletons of varied provenance had their sex determined by 15 existing methods of forensic anthropology (7 metric and 8 morphological). The methods were evaluated for their consistency in determination of sex. No single individual was identified as belonging to one sex exclusively. Ambiguous results were obtained by metric methods for fourteen individuals (70%) and by morphological methods for only five individuals (25%) (Chi-squared = 4.3, df = 1,
Determination of skeletal sex can be achieved using morphological (descriptive) or metric (quantitative) methods of forensic anthropology. Morphological methods rely on features which arise from an interaction between genetically controlled sex-linked patterns of growth and development, with environmental influences that may differ according to gender [
Numerous methods exist for determining skeletal sex; however, for the purposes of this study seven metric and eight morphological methods were chosen. The methods were included because they are widely used or cited, such as Acsadi and Nemeskeri [
Methods used for the determination of sex in this study.
Method number | Description of method | Collection used | Possible categories | Author and date |
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1 | 4x femoral measurements | Skeletal specimens from London, England | Female; cautiously female; ambiguous; cautiously male; male | Pearson and Bell 1917–1919 [ |
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2 | 5x talar/calcaneal discriminant functions | Terry Collection, Smithsonian Institution | Male or female | Steele 1976 [ |
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3 | 2x humeral discriminant functions | Dart Collection, University of Witwatersrand |
Male or female | Steyn and Işcan 1999 [ |
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4 | 2x cranial discriminant functions | Skeletal collection, University of Helsinki | Male or female | Kajanoja 1966 [ |
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5 | 5x cranial discriminant functions | Dart Collection, University of Witwatersrand | Male or female | Dayal et al. 2008 [ |
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6 | 5x scapular discriminant functions | Tell El-Armana burial site | Male or female | Dabbs 2010 [ |
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7 | 10x scapular discriminant functions | Skeletal collection, University of Bari | Male or female | Di Vella et al. 1994 [ |
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8 | 13x morphological traits of skull | Todd Collection, Western Reserve University | Male or female | Krogman and Iscan 1986 [ |
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9 | 16x morphological traits of pelvis | Todd Collection, Western Reserve University | Male or female | Krogman and Iscan 1986 [ |
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10 | Shape of greater sciatic notch | Hamann-Todd Collection, Cleveland |
Male; probable male/ambiguous; female | Walker 2005 [ |
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11 | Shape of ventral arc, subpubic concavity, ischiopubic ramus | Terry Collection, Smithsonian Institution | Male or female | Phenice 1969 [ |
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12 | Posterior mandibular ramus flexure | Dart Collection, University of Witwatersrand | Male or female | Loth and Henneberg 1996 [ |
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13 | Shape of olecranon fossa, angle of medial epicondyle, trochlear extension | Dart Collection, University of Witwatersrand |
Female; cautiously female; ambiguous; cautiously male; male | Vance et al. 2011 [ |
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14 | 22x morphological traits from the skull, pelvis, and femur | Secondary sources | Male or female | Acsadi and Nemeskeri 1970 [ |
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15 | 5x morphological traits of the skull, scored categorically for discriminant analysis | Hamann-Todd Collection, Cleveland |
Male or female | Walker 2008 [ |
This study used 20 skeletons held by Ray Last Laboratory at University of Adelaide. There was no selection; simply all available skeletons in the laboratory were used. The skeletons were of unknown sex, with one exception. This skeleton was recently acquired by dissection of a male cadaver. Although the sex of this skeleton was known, it was treated, in all analyses and interpretations, in the same manner as all other skeletons in this sample. For this study, knowledge of actual sex was not essential as this study aims to evaluate the consistency of results of various methods, rather than the competence of each single method. These skeletons are derived from a variety of populations. They come from two sources: (1) donated skeletons of Australians of European descent and (2) teaching skeletons bought by the university from India early in the 20th century. Some Australians of European descent may have a small admixture from Aboriginal Australians; this, however, is unlikely to influence their morphology. Since particular methods of sex estimation were based on skeletons from specific populations it is possible that they will not perform well on skeletons of different origins. The methods selected, chosen for this study, are those commonly used in forensic anthropology. These methods are based on a variety of United States, European, South African, and Egyptian skeletal series. To the author’s knowledge, there are not many methods based on skeletal series from Asia. Therefore, application of commonly used methods to Indian skeletons imitates a possible forensic situation where the population of origin of a skeleton is unknown and difficult to establish. The population of India is not easily defined as belonging to classic divisions of biological affinity, such as European/African/East Asian.
Fifteen methods were applied to the skeletal sample (Table
All assessments and measurements were conducted by a single observer (IS) to minimise interobserver errors. The first author is an osteologist, trained at a Master’s level. She is familiar with Martin’s technique of anthropometric measurements, which was designed to minimise measurement errors. Since we are testing actual forensic applications of methods of sex estimation, we did not include error estimates.
The ability of the methods to consistently determine the sex of an individual was evaluated in four different ways: (1) counting in how many cases the majority of methods gave the same result, that is, at least eight of the 15 methods identified the skeleton as belonging to the same sex; (2) counting in how many cases methods placed the sex of the same skeleton, into all three of the possible categories (male, female or ambiguous); (3) comparing the consistency between metric and morphological methods (this was achieved by counting how many times an individual was categorised as belonging to the same single sex by all seven metric methods or all 8 morphological methods); (4) counting in how many cases a single method resulted in ambiguity of sex estimation. This was achieved by evaluating the inconsistencies in estimations within an individual method, namely, those which present multiple opportunities for sex estimation.
The methods chosen utilise different skeletal elements to determine sex using different approaches to describing individual variation: categorical classification of morphological features or metric dimensions of skeletal elements. There is some overlap between specific methods in either skeletal elements used or methods of measurement. Thus the methods are only partly independent. We used nonparametric approach to measure interdependencies between specific methods; contingency table analyses producing Chi-squared values that allow the evaluation of statistical significance of differences, and when converted to Cramer’s
Tables
(a) Results of sex estimation of a series of skeletons by a number of metric methods recommended by forensic anthropology texts. Numbers (1), (2), and so forth in columns indicate results of different discriminant function equations by the same authors. (b) Results of sex estimation of a series of skeletons by a number of descriptive methods recommended by forensic anthropology texts. Numbers (1) and (2) in column 14 indicate results of two different discriminant function equations by the same author.
Methods | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ||
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Specimen number | Specimen label | Femoral dimensions | Talar/calcaneal discriminant functions | Humeral discriminant functions | Cranial discriminant functions | Cranial discriminant functions | Scapular discriminant functions | Scapular discriminant functions | |
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1 | A | (1) Male |
(1) Male |
(1) Male |
(1) Male |
(1) |
(1) Male |
(1) Male |
(6) Male |
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2 | B | (1) Male |
(1) Male |
(1) Male |
(1) Male |
(1) |
(1) Male |
(1) Male |
(6) Male |
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3 | 1 | (1) Female |
(1) Female |
(1) Female |
(1) Female |
(1) Female |
(1) Female |
(1) Female |
(6) Female |
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4 | 2 | (1) Cautiously female |
(1) Male |
(1) Female |
(1) Female |
(1) Male |
(1) Female |
(1) Female |
(6) Female |
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5 | 3 | (1) Male |
(1) Male |
(1) Male |
(1) Male |
(1) Male |
(1) Male |
(1) Female |
(6) Male |
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6 | 4 | (1) Male |
(1) Male |
( |
(1) Female |
(1) |
(1) Male |
(1) Female |
(6) Male |
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7 | 5 | (1) Male |
(1) Female |
(1) Female |
(1) Female |
(1) Male |
(1) Male |
(1) Female |
(6) Male |
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8 | 6 | (1) Ambiguous |
(1) Female |
(1) Female |
(1) Female |
(1) Female |
(1) Female |
(1) Female |
(6) Male |
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9 | 7 | (1) Cautiously female |
(1) Male |
(1) Female |
(1) Female |
(1) Male |
(1) Female |
(1) Female |
(6) Female |
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10 | AM1 | (1) Male |
(1) Male |
(1) Female |
(1) Female |
(1) Male |
(1) Male |
(1) Female |
(6) Male |
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11 | AM2 | (1) Cautiously female |
(1) Female |
(1) Female |
(1) Female |
(1) Male |
(1) Male |
(1) Female |
(6) Male |
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12 | AM3 | (1) Female |
(1) Male |
(1) Female |
(1) Female |
(1) Male |
(1) Female |
(1) Female |
(6) Female |
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13 | AM4 | (1) Female |
(1) Male |
(1) Female |
(1) Male |
(1) Male |
(1) Female |
(1) Female |
(6) Male |
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14 | AM5 | (1) Male |
(1) Male |
(1) Female |
(1) Female |
(1) Male |
(1) Male |
(1) Female |
(6) Male |
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15 | HS-041 | (1) Ambiguous |
(1) Male |
(1) Female |
(1) Male |
(1) Male |
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16 | HS-038 | (1) Cautiously female |
(1) Female |
(1) Female |
(1) Male |
(1) Male |
(1) Male |
(1) Female |
(6) Male |
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17 | HS-039 | (1) Ambiguous |
(1) Male |
(1) Female |
(1) Male |
(1) Male |
(1) Male |
(1) Female |
(6) Male |
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18 | HS-012 | (1) Cautiously female |
(1) Female |
(1) Male |
(1) Male |
(1) |
(1) Male |
(1) Female |
(6) Male |
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19 | SC-002 | (1) Female |
(1) Male |
(1) Female |
(1) Female |
(1) Male |
(1) Female |
(1) Female |
(6) Female |
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20 | SC-003 | (1) Female |
(1) Female |
(1) Female |
(1) Female |
(1) Female |
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Methods | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | |
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Specimen number | Specimen label | Cranial descriptive (morphological) traits | Pelvic descriptive (morphological) traits | Pelvic descriptive (morphological) trait | Pelvic descriptive (morphological) traits | Mandibular descriptive (morphological) traits | Score based on sexual dimorphism of humeral traits | Cranial, pelvic, and femoral descriptive (morphological) traits | Discriminant analysis of scored cranial descriptive (morphological) traits |
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1 | A | (i) 12/13 traits indicate male |
16/16 traits indicate male | (3) indicates male | 3/3 traits indicate male | (+2) indicates male | Score: 5/15 |
(0.91) indicates male | (1) Male |
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2 | B | (i) 10/12 |
(i) 12/16 traits indicate male |
(2) ambiguous | (i) 2/3 traits indicate male |
(+4) indicates male | Score: 6/15 |
(0.78) indicates male | (1) Male |
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3 | 1 | (i) 2/13 traits indicate male |
(i) 3/16 traits indicate male |
(2) ambiguous | 3/3 traits indicate female | (+2) indicates male | Score: 10/15 |
(−0.97) indicates female | (1) Female |
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4 | 2 | (i) 7/13 traits indicate male |
(i) 11/16 traits indicate male |
(4) indicates male | 3/3 traits indicate male | (+4) indicates male | Score: 6/15 |
(0.72) indicates male | (1) Male |
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5 | 3 | 13/13 traits indicate male | 16/16 traits indicate male | (4) indicates male | (i) 2/3 traits indicate male |
(+2) indicates male | Score: 6/15 |
(1.13) indicates male | (1) Male |
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6 | 4 | (i) 10/12 |
(i) 15/16 traits indicate male |
(2) ambiguous | 3/3 traits indicate male | ( |
Score: |
(0.52) indicates male | ( |
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7 | 5 | (i) 8/13 traits indicate male |
(i) 15/16 traits indicate male |
(4) indicates male | (i) 2/3 traits indicate male |
(−2) indicates female | Score: 4/15 |
(0.47) indicates male | (1) Male |
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8 | 6 | (i) 6/13 traits indicate male |
(i) 11/16 traits indicate male |
(5) indicates male | (i) 2/3 traits indicate male |
(−2) indicates female | Score: 7/15 |
(0.28) indicates male | (1) Male |
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9 | 7 | (i) 6/13 traits indicate male |
(i) 14/16 traits indicate male |
(4) indicates male | (i) 2/3 traits indicate male |
(+3) indicates male | Score: 6/15 |
(0.19) indicates male | (1) Male |
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10 | AM1 | (i) 8/13 traits indicate male |
(i) 14/16 traits indicate male |
(5) indicates male | 3/3 traits indicate male | (−2) indicates female | Score: 10/15 |
(0.59) indicates male | (1) Male |
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11 | AM2 | (i) 7/13 traits indicate male |
(i) 14/16 traits indicate male |
(4) indicates male | (i) 2/3 traits indicate male |
(+2) indicates male | Score: 6/15 |
(0.28) indicates male | (1) Male |
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12 | AM3 | (i) 10/13 traits indicate male |
(i) 11/16 traits indicate male |
(3) indicates male | 3/3 traits indicate male | (0) indicates male | Score: 10/15 |
(−0.25) indicates female | (1) Male |
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13 | AM4 | (i) 12/13 traits indicate male |
(i) 15/16 traits indicate male |
(5) indicates male | 3/3 traits indicate male | (+2) indicates male | Score: 7/15 |
(1.0) indicates male | (1) Male |
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14 | AM5 | (i) 10/13 traits indicate male |
(i) 15/16 traits indicate male |
(4) indicates male | (i) 2/3 traits indicate male |
(0) indicates male | Score: 7/15 |
(0.78) indicates male | (1) Male |
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15 | HS-041 | (i) 11/13 traits indicate male |
(i) 14/16 traits indicate male |
(5) indicates male | 3/3 traits indicate male | (+4) indicates male | Score: 6/15 |
(0.97) indicates male | (1) Male |
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16 | HS-038 | (i) 7/13 traits indicate male |
(i) 13/15 |
(3) indicates male | 3/3 traits indicate male | (+3) indicates male | Score: 4/15 |
(0.75) indicates male | (1) Male |
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17 | HS-039 | (i) 12/13 traits indicate male |
(i) 13/16 traits indicate male |
(3) indicates male | 3/3 traits indicate male | (+1) indicates male | Score: 6/15 |
(1.13) indicates male | (1) Male |
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18 | HS-012 | (i) 11/12 |
16/16 traits indicate male | (4) indicates male | 3/3 traits indicate male | ( |
Score: 5/15 |
(0.70) indicates male | ( |
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19 | SC-002 | (i) 3/13 traits indicate male |
(i) 13/16 traits indicate male |
(3) indicates male | 3/3 traits indicate male | (−2) indicates female | Score: 7/15 |
(−0.13) indicates female | (1) Male |
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20 | SC-003 | (i) 3/13 traits indicate male |
(i) 13/16 traits indicate male |
(3) indicates male | 3/3 traits indicate male | (+2) indicates male | Score: 4/15 |
(−0.09) indicates female | (1) Male |
Table
Similarity between results of various methods as measured by Cramer’s
Method | 1 QL | 3 QL | 7 QO | 10 DP | 4 QS | 9 DP | 11 DP | 15 DS | 6 QO | 5 QS | 8 DS | 13 DL | 14 DSPL | 12 DM | 2 QO |
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1 QL |
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3 QL |
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7 QO |
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0.67 | |||||||||||||
10 DP | 0.68 | 0.68 |
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4 QS |
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0.62 | 0.63 | ||||||||||
9 DP | 0.68 |
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11 DP | 0.68 |
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15 DS |
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0.69 |
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0.69 | 0.69 | 0.66 | |||||||
6 QO |
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5 QS | 0.67 |
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0.68 |
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8 DS |
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0.69 |
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13 DL |
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0.68 |
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14 DSPL |
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0.69 |
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12 DM | 0.62 |
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0.69 |
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2 QO | 0.63 |
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0.66 |
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Q = quantitative/metric methods; D = descriptive/morphological methods.
S = skull; L = long bones; M = mandible; P = pelvis; O = other bones.
In evaluation approach (1) 17 individuals (specimen numbers 1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 13, 14, 15, 16, 17, 18, and 19), shown in Tables
In evaluation approach (2) 14 individuals (specimen numbers 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, and 18), shown in Tables
In evaluation approach (3), Figure
(a) Consistency of metric methods in determination of sex in 20 skeletal cases. “A” is ambiguous, “F” is female, and “M” is male. (b) Consistency of morphological methods in determination of sex in 20 skeletal cases. “A” is ambiguous, “F” is female, and “M” is male.
In evaluation approach (4), Figure
Metric methods alone (Figure
The combination of the 15 methods used in this study did not produce a single, fully consistent identification of sex out of 20 skeletal cases. A limitation of this study remains to be that sex was only actually known in one of the 20 cases; however, this study’s aims were not to evaluate the ability of the methods individually; rather, they were to assess the consistency with which morphological and metric methods can determine skeletal sex. Therefore, knowledge of actual sex of any given skeleton was not essential.
The methods themselves are not completely independent of each other because some use the same body parts and the same/similar traits. Besides methods 9 (descriptive, pelvis) and 11 (descriptive, pelvis), similarities between results of methods are independent of the body part assessed and of the approach (quantitative or descriptive). For example, results of descriptive assessment of mandibular morphology are most similar to results of methods based on measurements of the skull, long bones, and other bones (Table
Table
A summary of methods in disagreement with a majority of sex estimates found in this study.
Skeletal element | Method | |
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Morphological (descriptive) | Metric (quantitative) | |
Cranial | 4 | 7 |
Pelvic | 7 | N/A |
Mandibular | 6 | N/A |
Humeral | 4 | 10 |
Femoral | N/A | 7 |
Talar/calcaneal | N/A | 4 |
Scapular | N/A | 10 |
Total | 21 | 38 |
Percentage out of all individual assessments | 21/140 |
38/160 |
Familiarity with distribution of sexual dimorphism in a particular single population may influence the judgements of an investigator. Investigators usually gain experience in assessing the range of sexual dimorphism in the particular populations they frequently work with. When faced with a need for a sex estimate from a skeleton of unknown population of origin, even with the best intentions, their experience may result in a bias. In the case of this study, this bias was avoided because IS, although fully trained in methods of sex and age estimation, had no experience working for a substantial time with any single, specific skeletal sample from a particular population.
A larger sample size may have enabled a consistent determination of sex to occur although the fact that this was not seen in 20 skeletal cases is cause for concern. In forensic proceedings the standard of evidence required is “beyond reasonable doubt,” and in this study significant doubt is evident. As mentioned earlier, this study assesses the consistency of 15 out of many available methods. It may be argued that this subset cannot provide an accurate representation of all available methods; however, with results showing a 0% reliability rate of the consistency between many methods used, one can assume that if more methods were used, lack of consistency would have persisted. This is following the assumption that the ancestry of the skeleton/s under investigation is unknown and therefore, the methods chosen may be based on little more than an educated guess. Anthropologists with an experience of working in a particular geographic area may develop a good understanding of local patterns of variation that will allow them to choose the most appropriate sexing methods to suit their conditions. This, however, may not always be the case, especially in highly mobile societies or when an anthropologist is studying a series of skeletal remains of an unfamiliar area. Increasingly, courts of law require that experts provide objective proof of their statements rather than simply expressing an opinion based on their experience. A method of sex estimation in a sample from a particular population, that is independent of population-specific biases, inherent in existing methods, has been proposed as early as the 1950’s [
Currently, it is thought that the morphological indicators provide the greatest discrimination between the sexes, that is, the pelvis and the skull, with 95% and 90% accuracy, respectively [
This study employed methods that are being used currently in forensic investigations and they failed to provide consistent identification of sex in all 20 cases, including the one skeleton of known sex. Seventeen individuals (85%) were found to be by “majority” one sex. This study considers it “majority” when at least eight of the 15 total methods produce the same result. Of the 17 skeletal cases which were found to be by majority one sex, four cases had a majority of 14, one had a majority of 13, three had a majority of 12, three had a majority of 11, two had a majority of 10, three had a majority of nine, and one had a majority of eight. The determination of skeletal sex, in a particular case, may depend on the method used by forensic investigators. This is especially highlighted by three cases (specimens 8, 12, and 20), where individuals did not have a majority of methods indicating clearly one sex. Forensic investigators are guided in the choice of the method by a possible population to which the investigated individual may belong. This increases reliability of a sex estimate but does not always guarantee it.
When comparing Figures
Figure
Comparison of the consistency of all metric and all morphological methods. “M” is male, “F” is female, and “A” is ambiguous.
Determination of skeletal sex is often the first biological characteristic sought after by forensic investigators in cases of discovery of skeletal remains. In methods of sex estimation characteristics that may result from specific gender roles in particular populations, as well as those related to overall size of individuals, seem to be least useful when a population of origin is not known. The search for characteristics reflecting, as directly as possible, the influence of sex hormones on development of skeletal morphology, irrespective of an individual’s size, may produce most generally applicable methods. Also, technologies enabling better observation of morphological characteristics, for example, geometric morphometrics, may be used to quantify shape of rigid structures that are often curved and are not easily measured using standard metric methods [
See Table
Comparison of the consistency between morphological (descriptive) and metric methods, where M = male; F = female; A = ambiguous.
Specimen number | Specimen label | Morphological (descriptive) methods (out of 8) | Metric methods (out of 7) | All methods (out of 15) | ||||||
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M | F | A | M | F | A | M | F | A | ||
1 | A | 7 | 1 | 7 | 14 | 1 | ||||
2 | B | 7 | 1 | 7 | 14 | 1 | ||||
3 | 1 | 1 | 6 | 1 | 7 | 1 | 13 | 1 | ||
4 | 2 | 8 | 1 | 4 | 2 | 9 | 4 | 2 | ||
5 | 3 | 8 | 6 | 1 | 14 | 1 | ||||
6 | 4 | 4 |
1 |
4 |
2 |
8 |
2 |
1 |
||
7 | 5 | 7 | 1 | 4 | 2 | 1 | 11 | 3 | 1 | |
8 | 6 | 6 | 2 | 5 | 2 | 6 | 7 | 2 | ||
9 | 7 | 7 | 1 | 2 | 3 | 2 | 9 | 4 | 2 | |
10 | AM1 | 6 | 2 | 4 | 2 | 1 | 10 | 4 | 1 | |
11 | AM2 | 8 | 3 | 3 | 1 | 11 | 3 | 1 | ||
12 | AM3 | 5 | 2 | 1 | 1 | 5 | 1 | 6 | 7 | 2 |
13 | AM4 | 8 | 4 | 2 | 1 | 12 | 2 | 1 | ||
14 | AM5 | 8 | 4 | 1 | 2 | 12 | 1 | 2 | ||
15 | HS-041 | 8 | 3 |
2 |
11 |
2 |
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16 | HS-038 | 8 | 4 | 2 | 1 | 12 | 2 | 1 | ||
17 | HS-039 | 8 | 3 | 2 | 2 | 11 | 2 | 2 | ||
18 | HS-012 | 6 |
4 | 1 | 2 | 10 |
1 |
2 |
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19 | SC-002 | 5 | 3 | 1 | 6 | 6 | 9 | |||
20 | SC-003 | 6 | 2 | 5 |
6 |
7 |
The authors declare that there is no conflict of interests regarding the publication of this paper.
This paper is dedicated to the memory of the late Dr. Susan R. Loth who contributed heavily to the thoughts expressed here.