Metacarpal sexual determination in a Spanish population

Machine Learning Models for Prediction of Sex Based on Lumbar Vertebral Morphometry

BACKGROUND

Identifying skeletal remains has been and will remain a challenge for forensic experts and forensic anthropologists, especially in disasters with multiple victims or skeletal remains in an advanced stage of decomposition. This study examined the performance of two machine learning (ML) algorithms in predicting the person's sex based only on the morphometry of L1-L5 lumbar vertebrae collected recently from Romanian individuals. The purpose of the present study was to assess whether by using the machine learning (ML) techniques one can obtain a reliable prediction of sex in forensic identification based only on the parameters obtained from the metric analysis of the lumbar spine.

METHOD

This paper built and tuned predictive models with two of the most popular techniques for classification, RF (random forest) and XGB (xgboost). Both series of models used cross-validation and a grid search to find the best combination of hyper-parameters. The best models were selected based on the ROC_AUC (area under curve) metric.

RESULTS

The L1-L5 lumbar vertebrae exhibit sexual dimorphism and can be used as predictors in sex prediction. Out of the eight significant predictors for sex, six were found to be particularly important for the RF model, while only three were determined to be important by the XGB model.

CONCLUSIONS

Even if the data set was small (149 observations), both RF and XGB techniques reliably predicted a person's sex based only on the L1-L5 measurements. This can prove valuable, especially when only skeletal remains are available. With minor adjustments, the presented ML setup can be transformed into an interactive web service, freely accessible to forensic anthropologists, in which, after entering the L1-L5 measurements of a body/cadaver, they can predict the person's sex.

Sex Determination According to the Lengths of Hand Bones in Rhesus Macaques (Macaca Mulatta)

Measurement of hand bone length has been used for sex determination in humans and nonhuman primates (McFadden and Bracht: Early Hum Dev 85 (2009) 117-124; El-Morsi and Al-Hawary: J Forensic Leg Med 20 (2013) 6-13). The aim of this study was to determine the sex of rhesus macaques (Macaca mulatta) on the basis of the lengths of corresponding rows of metacarpals and phalanges in a macaque population by means of developing discriminant functions. Measurements on direct dry bones only included lengths for 19 bones of the left hand in 39 macaques (consisting of 13 adult males and 26 adult females). The results revealed that the mean values of males were significantly greater than those of females for all of the metacarpals and phalanges. The results were obtained in 84.4% of accuracy from distal phalanges, 93.8% from middle phalanges, and 96.9% from both metacarpals and proximal phalanges, respectively. There was a remarkable difference in the magnitude of sex dimorphism in lengths of each section of the hand bones between the population of macaques and humans. This difference may be attributable to the interaction between genetic factors and various environmental factors. As sex differences of hand bones are population-specific (Lazenby: Am J phys Anthropol 118 (2002) 378-384; Lu, Huo, Shi, Peng, Dang, Jiao, Zhu, Zhong, and Chen: Acta Aantomica Sinica 39 (2008) 267-271; Eshak, Ahmed, and Gawad: J Forensic Leg Med 18 (2011) 246-252), the discriminant equations for all of the metacarpals and phalanges are applicable to the population of Macaca mulatta from the Taihang Mountain. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1741-1746, 2017. © 2017 Wiley Periodicals, Inc.

Sex estimation from the navicular bone in Spanish contemporary skeletal collections

Sexual estimation is fundamental to reconstruct the biological profile of individuals, but postdepositional factors can alter the resistance of the bones, thereby preventing accurate diagnosis especially when the skull and the pelvis are absent. Navicular bones are usually well preserved in archeological and forensic contexts and can a good alternative to discriminate sex. On the basis of these aspects, the present investigation analyzed the sexual dimorphism in 231 pairs of navicular bones from documented contemporary collections from Spain. Receiver operating characteristic (ROC) curve analysis and binary logistic regressions were carried out in eight replicable linear measurements of the navicular bone. Each of the eight variables showed a significant sexual dimorphism in our sample. The ROC curve results indicate that at least five out of the eight variables used have high ability for sex diagnosis, among which the maximum length of the cuneiform surface (LMAXCUN) showed a better performance (area under the curve value=0.86). Moreover, we introduced regression equations with combination of measurements that correctly allocated the skeletons with 80% or greater accuracy. The equation with high allocation accuracy rate (83.4%) included a combination of the maximum height of the navicular (HMAX), maximum length of the cuneiform surface (LMAXCUN), and maximum length of the talar facet (LMAXTAL). The regression equations presented here are useful for the Western Mediterranean populations and offer better alternatives than formulas based on other population groups.

Measurement standards for human metacarpals

Standards for measuring the metacarpals are absent from commonly used osteometric guides. Perhaps the closest to a set of standard measurements in common use today are those proposed by Scheuer and Elkington (Scheuer and Elkington: J Forensic Sci 38 (1993) 769-788) for forensic sex assessment. They include caliper measurements of interarticular length, base and head width, base and head height, and maximum midshaft diameter. Over the last decade, a new set of measurements that encompass similar dimensions to those used by Scheuer and Elkington, but which are taken with a mini-osteometric board (MOB) have been developed by the lead author. Use of the MOB avoids the need to manipulate both the bone and calipers in three-dimensional space and causes less strain on the hands. However, the question of intra- and interobserver accuracy has not been adequately addressed for either set of measurements. The purpose of this study was to test both the Scheuer/Elkington and MOB measurements on 20 hands from 10 anatomical skeletons for intra- and inter-observer accuracy. The study found that 92% of the MOB measures had a lower intraobserver error, and 88% had a lower interobserver error than did the caliper measurements. It also found that the maximum midshaft diameter measurement used by Scheuer and Elkington is more repeatable than a mediolateral diameter. Overall, 88% of the 25 MOB measurements had median intraobserver error rates of under 1.5%, compared with 60% of the caliper measurements. Furthermore, the MOB measurements as a set were taken 10 to 12% faster than the caliper measurements.

Sex determination by discriminant function analysis of lumbar vertebrae

Sex determination is critical for developing the biological profile of unidentified skeletal remains. When more commonly used elements (os coxa, cranium) for sexing are not available, methods utilizing other skeletal elements are needed. This study aims to assess the degree of sexual dimorphism of the lumbar vertebrae and develop discriminant functions for sex determination from them, using a sample of South African blacks from the Raymond A. Dart Collection (47 males, 51 females). Eleven variables at each lumbar level were subjected to univariate and multivariate discriminant function analyses. Univariate equations produced classification rates ranging from 57.7% to 83.5%, with the highest accuracies associated with dimensions of the vertebral body. Multivariate stepwise analysis generated classification rates ranging from 75.9% to 88.7%. These results are comparable to other methods for sexing the skeleton and indicate that measures of the lumbar vertebrae can be used as an effective tool for sex determination.

Statistical sex determination from craniometrics: Comparison of linear discriminant analysis, logistic regression, and support vector machines

Accuracy of identification tools in forensic anthropology primarily rely upon the variations inherent in the data upon which they are built. Sex determination methods based on craniometrics are widely used and known to be specific to several factors (e.g. sample distribution, population, age, secular trends, measurement technique, etc.). The goal of this study is to discuss the potential variations linked to the statistical treatment of the data. Traditional craniometrics of four samples extracted from documented osteological collections (from Portugal, France, the U.S.A., and Thailand) were used to test three different classification methods: linear discriminant analysis (LDA), logistic regression (LR), and support vector machines (SVM). The Portuguese sample was set as a training model on which the other samples were applied in order to assess the validity and reliability of the different models. The tests were performed using different parameters: some included the selection of the best predictors; some included a strict decision threshold (sex assessed only if the related posterior probability was high, including the notion of indeterminate result); and some used an unbalanced sex-ratio. Results indicated that LR tends to perform slightly better than the other techniques and offers a better selection of predictors. Also, the use of a decision threshold (i.e. p>0.95) is essential to ensure an acceptable reliability of sex determination methods based on craniometrics. Although the Portuguese, French, and American samples share a similar sexual dimorphism, application of Western models on the Thai sample (that displayed a lower degree of dimorphism) was unsuccessful.

Estimation of sex from the metric assessment of digital hand radiographs in a Western Australian population

The forensic anthropologist is responsible for contributing to the identification of an unknown by constructing a biological profile from their skeletal remains. Towards achieving this goal, anthropologists can apply population and temporally specific standards with known error margins to morphometric data collected from a decedent. Recent research relating to the formulation of sex estimation standards has focussed on the assessment of bones other than the traditionally favoured pelvis and cranium, such as long bones of the appendicular skeleton. In particular, sex estimation standards based on morphometric data from metacarpals and phalanges have reported classification accuracy rates of 80% (and above) based on a narrow range of populations. The purpose of this study is to provide population-specific hand bone sex-estimation standards for a contemporary Western Australian population. The present study examines digital right hand radiographs of 300 adults of known age, equally represented by sex. A total of 40 measurements were taken in each hand (metacarpals and proximal phalanges); the measurements were then analysed using univariate statistics and cross-validated direct and stepwise discriminant function analysis. All hand bone measurements were significantly sexually dimorphic, with a tendency for the width measurements to express a higher degree of dimorphism than the length measurements. A maximum cross-validated classification accuracy of 91% was achieved with a sex bias of -6%. The standards presented here can be used in future forensic investigations that require sex estimation of hand bones in a Western Australian population.

Sex and age related non-metric variation of the human sternum in a Northwest Indian postmortem sample: a pilot study

Nonmetric traits are quasi-continuous skeletal traits that cannot be measured, but are observed as ranks or scores. In the present study, 8 nonmetric traits of sternum were examined from 343 sternums collected from the autopsy cases. More males, particularly older subjects, had a mesosternal foramen. The frequency of mesosternal foramen, arch-shaped prominence on the manubrium and radial strips on mesosternum significantly increased but that of lateral projection of manubrium decreased in the 30+ year age-group (older individuals). The denticulate costal incisures were found mostly in females and younger subjects; however, the crescent incisures and arch shaped prominence of manubrium were noticed mainly in males and older subjects. Majority of subjects had 'deep and narrow' jugular notch and xiphi-sternum was 'bifid' or 'oblong' in males and 'small sized' in females and younger subjects. Xiphi-sternum was generally found absent in females and younger subjects. The different shapes of costal incisures, jugular notch and xiphoid process were found to have significant sex and age differences. The number of cases with fused elements significantly increased with advancing age in both sexes. The sternal elements' fusion showed a variable pattern and hence was not found to be a reliable criterion. Chi-square analysis revealed significant differences between two age-groups of individual sex in the distribution of 3 of the 8 nonmetric traits. Significant sex and age differences were noticed in the frequency of occurrence of mesosternal foramina between the younger and older age groups in both the sexes. The logistic regression analysis of the scores classified 73.8% sternums to their sex category and 70.0% sternums to their age-group. Though present findings may not be enough for absolute personal identification, these traits can still serve as important identification tools if antemortem radiographs/CT or MRI scans are available for comparisons, or help classify an unknown sternum to its sex or age category based on the morphological features discussed in present study.

Sex determination by the length of metacarpals and phalanges: X-ray study on Egyptian population

Measurements of hand bones length have been shown to be sexually dimorphic in many nationalities. The aim of this study is to assess the accuracy of sex determination from the length of all metacarpals and phalanges of right and left hands using X-ray radiographs and to develop a discriminant formula that can be used in the Egyptians. One hundred Egyptians are included in the study (50 adult males and 50 adult females) in the period from December 2009 to January 2011 with mean age 31.60 ± 9.44. Each is subjected to X-ray radiographs on both hands. The results reveal that males have significantly greater mean values than females for all metacarpals and phalanges of both hands and the Egyptian population has greater measurements in comparison to the other ones (e.g. Turkish and European Americans). In addition there is no significant difference between the right and the left hands in either males or females. The correct classification reached an accuracy of 88%-94% by using both hands, while that for right hand only is 88% and 88%-90% for the left hand only. Regarding the accuracy of each bone, the present results revealed that 1st DP & PP and 3rd and 4th MC in the right and left hands are the best bones that can be used in correct sex determination. It is concluded that the length of metacarpals and phalanges (especially the 1st DP & PP and 3rd and 4th MC) could be used for sex determination. The right hand could be used as the left hand in determination of sex. Also the X-ray radiographs are good non invasive and simple tool in the determination of sex from the hand bones. Furthermore the regression equation for both hands and each hand separately is specific to Egyptian population and should be used after validation of the results in other ones.

Sex determination by discriminant function analysis of palatal rugae from a population of coastal Andhra

OBJECTIVE

The aim of the study was to investigate differences in the palatal rugae patterns in males and females of a cross-sectional hospital-based coastal Andhra population and application of discriminant function analysis in sex identification.

MATERIALS AND METHODS

One hundred pre-orthodontic plaster casts, equally distributed between males and females belonging to an age range of 15-30 years, were examined for different rugae patterns. Thomas classification was adopted for analysis. Association between rugae patterns and sexual dimorphism were tested using Unpaired t test, Chi square test and discriminant function analysis developed using SAS package.

RESULTS

Difference in unification pattern among males and females was found to be statistically significant. The total number of the rugae was not statistically significant between the sexes. Association between rugae length and shape with sex determination was computed using discriminant analysis which enabled sex differentiation in this population with an accuracy of 78%.

CONCLUSION

Palatal rugae revealed a specific pattern in unification among males and females of the coastal Andhra population. Discriminant function analysis enabled sex determination of individuals. However, these interpretations were precluded by the small sample size and further research work on larger samples and use of different classification systems is required to validate its use in forensic science.

Anthropometry of hand in sex determination of dismembered remains - A review of literature

Sex determination is an important and one of the foremost criteria in establishing the identity of an individual. Identification of dismembered/severed human remains that are frequently found in cases of mass disasters and criminal mutilation is a challenging task for the medicolegal experts. The paper presents a review of anthropometric studies conducted on hand with regard to identification of the deceased from dismembered remains. The review further discusses the anthropometric landmarks, techniques, methods, reliability and accuracy and the overall significance of hand anthropometry in personal identification. This review is an attempt to discuss the sexual dimorphism exhibited by the anthropometry of the hand that can assist forensic experts in the identification of amputated/dismembered remains.

Three-dimensional geometric morphometric analysis of cranio-facial sexual dimorphism in a Central European sample of known sex

This article presents an approach for estimating the sexual dimorphism of adult crania using three-dimensional geometric morphometric methods. The study sample consisted of 139 crania of known sex (73 males and 66 females) belonging to persons who lived during the first half of the 20th century in Bohemia. The three-dimensional co-ordinates of 82 ecto-cranial landmarks and 39 semi-landmarks covering the midsagittal curve of the cranial vault were digitised using a MicroScribe G2X contact digitiser. The purposes of the investigation were to define the regions of the cranium where sexual dimorphism is most pronounced and to investigate the effectiveness of this method for determining sex from the shape of the cranium. The results demonstrate that it is better to analyse apportionable parts of the cranium rather than the cranium as a whole. Significant sexual differences (significance was determined using multivariate analysis of variance) were noted in the shape of the midsagittal curve of the vault, upper face, the region of the nose, orbits, and palate. No differences were recorded either in the shape of the cranium as a whole or in the regions of the base and the neurocranium. The greatest accuracy in determining sex was found in the region of the upper face (100% of study subjects correctly classified) and the midsagittal curve of the vault (99% of study subjects correctly classified).