Forensic Anthropology Data Bank Research Articles

Classification of Malaysian individuals using Fordisc 3 based on four craniofacial measurements

ABSTRACT Fordisc is a discriminant function computer program used to study ancestry, although it lacks representation from a Malaysian sample. Our aim was to evaluate ancestry estimates of Fordisc 3 with Malaysian crania of known sex and ethnicity. A dataset from Hisham and Ibrahim of 300 individuals was included in this study. They had undergone full-body computed tomographic scanning prior to post-mortem examination with scan resolutions of 1.0 mm. Maximum cranial length, maximum cranial breadth, nasal height, nasal breadth, and midorbital width were obtained from these images. Measurements were fed into the Fordisc 3 program and were analysed using the Forensic Anthropology Data Bank (FDB) and Howells’ reference populations according to sex, however midorbital width was excluded in all analyses. Ancestry assessment was evaluated on the basis of percentage of correctly classified individuals. Based on Howells database, 50.67% of the sample are correctly classified into Asian, in contrast to only 32.33% according to FDB. These classification trends are limited by the number of measurements, reference populations available in Fordisc and population history of the sample itself. We need to collect standard anthropological measurements in future research and potentially contribute to the database in Fordisc to improve its performance.

Survivability versus rate of recovery for skeletal elements in forensic anthropology.

Survivability, the ability of a skeletal element to withstand taphonomic processes, is often equated to recoverability, the probability that an element will be recovered in a forensic context, and further misused to infer the likelihood that a forensic anthropologist will recover a particular element at a scene. Consequently, researchers have utilized notions of survivability to infer that a skeletal element may be recovered when justifying the necessity of various research endeavors. This is problematic because the factors impacting survivability are not always applicable in a forensic context; the ability of a bone to survive taphonomic processes may not align with the likelihood of recovery. Empirical recovery rates are presented from two distinct contexts, with data derived from the Forensic Anthropology Data Bank based on cases performed by the late J. Lawrence Angel (1914-1986) and cases done by the University of Tennessee Knoxville (UTK). Recovery rates may be influenced by factors beyond survivability, though we do not investigate the many considerations that might explain recovery rate variation between datasets. Rather, these data exemplify the conceptual differences between notions of survivability and rates of recovery in actual casework scenarios. Thus, it is proposed that researchers consider documented rates of recovery when providing rationale for forensic anthropology research endeavors, in addition to citing a rationale that is based on inferences of survivability. This ensures that the theoretical framework of future forensic anthropology research stems, primarily, from the premise of practical application.

Can we refine body mass estimations based on femoral head breadth?

Femoral head breadth is widely used in body mass estimation in biological anthropology. Earlier research has demonstrated that reduced major axis (RMA) equations perform better than least squares (LS) equations. Although a simple RMA equation to estimate body size from femoral head breadth is sufficient in most cases, our experiments with male skeletons from European data (including late Pleistocene and Holocene skeletal samples) and the Forensic Anthropology Data Bank data (including the W. M. Bass Donated Skeletal Collection sample) show that including femoral length or anatomically estimated stature in an equation with femoral head breadth improves body mass estimation precision. More specifically, although directional bias related to body mass is not reduced within specific samples, the total estimation error range, directional bias related to stature, and temporal fluctuation in estimation error are markedly reduced. The overall body mass estimation precision of individuals representing different temporal periods and ancestry groups (e.g., African and European ancestry) is thus improved.

Population inference from contemporary American craniometrics.

This analysis delivers a composite picture of population structure, admixture, ancestry variation, and personal identity in the United States, as observed through the lens of forensic anthropological casework and modern skeletal collections. It tests the applicability of the probabilistic clustering methods commonly used in human population genetics for the analysis of continuous, cranial measurement data, to improve population inference for admixed individuals without prior knowledge of sample origins. The unsupervised model-based clustering methods of finite mixture analysis are used here to reveal latent population structure and generate admixture proportions for craniofacial measurements from the Forensic Anthropology Data Bank (FDB). Craniometric estimates of ancestry are also generated under a three contributor model, sourcing parental reference populations from the Howells Craniometric Dataset. Tests of association are made among the coefficients of cluster memberships and the demographic information documented for each individual in the FDB. Clustering results are contextualized within the framework of conventional approaches to population structure analysis and individual ancestry estimation to discuss method compatibility. The findings reported here for contemporary American craniometrics are in agreement with the expected patterns of intergroup relationships, geographic origins and results from published genetic analyses. Population inference methods that allow for the model-bound estimation of admixture and ancestry proportions from craniometric data not only enable parallel-skeletal and genetic-analyses but they are also shown to be more informative than those methods that perform hard classifications using externally-imposed categories or seek to explain gross variation by low-dimensional projections. Am J Phys Anthropol 160:604-624, 2016. © 2016 Wiley Periodicals, Inc.

Changes in Clavicle Length and Maturation in Americans: 1840–1980

Secular changes refer to short-term biological changes ostensibly due to environmental factors. Two well-documented secular trends in many populations are earlier age of menarche and increasing stature. This study synthesizes data on maximum clavicle length and fusion of the medial epiphysis in 1840-1980 American birth cohorts to provide a comprehensive assessment of developmental and morphological change in the clavicle. Clavicles from the Hamann-Todd Human Osteological Collection (n = 354), McKern and Stewart Korean War males (n = 341), Forensic Anthropology Data Bank (n = 1,239), and the McCormick Clavicle Collection (n = 1,137) were used in the analysis. Transition analysis was used to evaluate fusion of the medial epiphysis (scored as unfused, fusing, or fused). Several statistical treatments were used to assess fluctuations in maximum clavicle length. First, Durbin-Watson tests were used to evaluate autocorrelation, and a local regression (LOESS) was used to identify visual shifts in the regression slope. Next, piecewise regression was used to fit linear regression models before and after the estimated breakpoints. Multiple starting parameters were tested in the range determined to contain the breakpoint, and the model with the smallest mean squared error was chosen as the best fit. The parameters from the best-fit models were then used to derive the piecewise models, which were compared with the initial simple linear regression models to determine which model provided the best fit for the secular change data. The epiphyseal union data indicate a decline in the age at onset of fusion since the early twentieth century. Fusion commences approximately four years earlier in mid- to late twentieth-century birth cohorts than in late nineteenth- and early twentieth-century birth cohorts. However, fusion is completed at roughly the same age across cohorts. The most significant decline in age at onset of epiphyseal union appears to have occurred since the mid-twentieth century. LOESS plots show a breakpoint in the clavicle length data around the mid-twentieth century in both sexes, and piecewise regression models indicate a significant decrease in clavicle length in the American population after 1940. The piecewise model provides a slightly better fit than the simple linear model. Since the model standard error is not substantially different from the piecewise model, an argument could be made to select the less complex linear model. However, we chose the piecewise model to detect changes in clavicle length that are overfitted with a linear model. The decrease in maximum clavicle length is in line with a documented narrowing of the American skeletal form, as shown by analyses of cranial and facial breadth and bi-iliac breadth of the pelvis. Environmental influences on skeletal form include increases in body mass index, health improvements, improved socioeconomic status, and elimination of infectious diseases. Secular changes in bony dimensions and skeletal maturation stipulate that medical and forensic standards used to deduce information about growth, health, and biological traits must be derived from modern populations.

An alternative approach for estimating stature from long bones that is not population- or group-specific

An accurate and precise estimate of stature can be very useful in the analysis of human remains in forensic cases. A problem with many stature estimation methods is that an unknown individual must first be assigned to a specific group before a method can be applied. Group membership has been defined by sex, age, year of birth, race, ancestry, continental origin, nationality or a combination of these criteria. Univariate and multivariate sex-specific and generic equations are presented here that do not require an unknown individual to be assigned to a group before stature is estimated. The equations were developed using linear regression with a sample (n=244) from the Terry Collection and tested using independent samples from the Forensic Anthropology Databank (n=136) and the Lisbon Collection (n=85). Tests with these independent samples show that (1) the femur provides the best univariate results; (2) the best multivariate equation includes the humerus, femur and tibia lengths; (3) a generic equation that does not require an unknown to first be assigned to a given category provides the best results most often; (4) a population-specific equation does not provide better results for estimating stature; (5) sex-specific equations can provide slightly better results in some cases; however, estimating the wrong sex can have a negative impact on precision and accuracy. With these equations, stature can be estimated independently of age at death, sex or group membership.

Postcranial Sex Estimation of Individuals Considered Hispanic

When forensic anthropologists estimate the sex of Hispanic skeletal remains using nonpopulation specific metric methods, initial observations cause males to frequently misclassify as female. To help improve these methods, this research uses postcranial measurements from United States-Mexico border migrant fatalities at the Pima County Office of the Medical Examiner in Tucson, Arizona, as well as Hispanic individuals from the Forensic Anthropology Data Bank. Using a total of 114 males and 28 females, sectioning points and discriminant functions provide classification rates as high as 89.43% for Hispanic individuals. A test sample assessed the reliability of these techniques resulting in accuracy up to 99.65%. The clavicle maximum length measurement provides the best univariate estimate of sex, while the radius provides the best multivariate estimated of sex. The results of this research highlight the need for population specific data in the creation of a biological profile, especially when working with individuals considered Hispanic.

Sex estimation in forensic anthropology: skull versus postcranial elements.

When the pelvis is unavailable, the skull is widely considered the second best indicator of sex. The goals of this research are to provide an objective hierarchy of sexing effectiveness of cranial and postcranial elements and to test the widespread notion that the skull is superior to postcranial bones. We constructed both univariate and multivariate discriminant models using data from the Forensic Anthropology Data Bank. Discriminating effectiveness was assessed by cross-validated classification, and in the case of multivariate models, Mahalanobis D(2). The results clearly indicate that most postcranial elements outperform the skull in estimating sex. It is possible to correctly sex 88-90% of individuals with joint size, up to 94% with multivariate models of the postcranial bones. The best models for the cranium do not exceed 90%. We conclude that postcranial elements are to be preferred to the cranium for estimating sex when the pelvis is unavailable.

Evaluation of Stature Estimation from the Database for Forensic Anthropology*†

Trotter and Gleser's (1-3) stature equations, conventionally used to estimate stature, are not appropriate to use in the modern forensic context. In this study, stature is assessed with a modern (birth years after 1944) American sample (N = 242) derived from the National Institute of Justice Database for Forensic Anthropology in the United States and the Forensic Anthropology Databank. New stature formulae have been calculated using forensic stature (FSTAT) and a combined dataset of forensic, cadaver, and measured statures referred to as Any Stature (ASTAT). The new FSTAT-based equations had an improved accuracy in Blacks with little improvement over Ousley's (4) equations for Whites. ASTAT-based equations performed equal to those of FSTAT equations and may be more appropriate, because they reflect both the variation in reported statures and in cadaver statures. It is essential to use not only equations based on forensic statures, but also equations based on modern samples.

Demographic Change and Forensic Identification: Problems in Metric Identification of Hispanic Skeletons*

The United States (U.S.) population structure is currently in a state of flux with one of the most profound changes being the increasing number of people referred to as Hispanic. In the U.S., much of the identification criteria for a biological profile are based on American Black and White individuals from anatomical collections. Using metric data from the Forensic Anthropology Data Bank (FDB), this paper will attempt to explore several issues that forensic anthropologists face when confronted with Hispanic remains. These will involve estimation of sex, height, and ancestry, the initial components of a biological profile. Discriminant function analyses indicate that American White criteria provide poor estimations of sex when applied to Hispanics and that ancestry estimation of Hispanic crania is difficult. Additionally, a new linear regression equation is presented that estimates stature for Hispanic individuals, although population specific criteria are still needed for Hispanic individuals from diverse geographical origins.

Cranial Change in Americans: 1850–1975

This paper examines the pattern and magnitude of craniofacial change in American blacks and whites over the past 125 years. Standard metric data from 885 crania were used to document the changes from 1850 to 1975. Data from 19th century crania were primarily from anatomical collections, and 20th century data were available from the forensic anthropology data bank. Canonical correlation was used to obtain a linear function of cranial variables that correlates maximally with year of birth. Canonical correlations of year of birth with the linear function of cranial measurements ranged from 0.55 to 0.71, demonstrating that cranial morphology is strongly dependent on year of birth. During the 125 years under consideration, cranial vaults have become markedly higher, somewhat narrower, with narrower faces. The changes in cranial morphology are probably in large part due to changes in growth at the cranial base due to improved environmental conditions. The changes are likely a combination of phenotypic plasticity and genetic changes over this period.

Secular change in craniofacial morphology.

Five craniofacial variables (glabella-occipital length, basion-bregma height, maximum cranial breadth, nasion-prosthion height, and bizygomatic breadth) were used to examine secular change in morphology from the mid-19(th) century to the 1970s. The 19(th) century data were obtained from the Terry and Hamann-Todd anatomical collections, and the 20(th) century data were obtained from the forensic anthropology databank. Data were available for Blacks and Whites of both sexes. Secular change was evaluated by regressing cranial variables on year of birth. Two analyses were conducted, one using the original variables and one using size and shape. Size is defined as the geometric mean of the cranial variables, and shape is the ratio of each variable to size. The results show remarkable changes in the size and shape of the cranial vault. Vault height increases in all groups in both absolute and relative terms. The vault also becomes longer and narrower, but these changes are less pronounced. Face changes are less than the vault changes, but to the extent that they occur, the face becomes narrower and higher. Overall cranial vault size has increased, but shape changes are greater than size changes. The magnitude of secular change in vault height exceeds that for long bones over a comparable time period, but follows a similar course, which suggests that vault height and bone length respond to the same forces. Changes in vault dimensions must occur by early childhood because of the early development of the vault. Am. J. Hum. Biol. 12:327-338, 2000. Copyright 2000 Wiley-Liss, Inc.

Secular change in long bone length and proportion in the United States, 1800-1970.

We examine secular change in long bone lengths and allometry of Americans dating from the mid-19th century to the 1970s. Skeletal samples were derived from the Huntington Collection, Terry Collection, World War II casualties, and the Forensic Anthropology Data Bank. Regression of bone length on year of birth allowed evaluation of the secular change in bone length. Size was computed as the geometric mean of all bone lengths, and shape as the ratio of each bone to size. These variables were then regressed on year of birth, allowing evaluation of allometric secular change. The results revealed a pattern of change that can be summarized as follows: male secular change is stronger than female, lower limb bone secular change is more pronounced than upper limb bone change, and distal bones change more than proximal bones, particularly in the lower limb. In males, white changes are uniformly higher than black but these differences do not rise to the level of statistical significance. Environmental forces, such as nutrition and disease, are the usual causes of secular changes in overall size. This paper shows that long bone proportions also respond to these same environmental factors. Moreover, the changes in body proportion are likely to be due to allometric consequences of growth changes that occur early in life. Am J Phys Anthropol 110:57-67, 1999.

Osteometric Analysis of Sexual Dimorphism in the Sternal End of the Rib in a West African Population

This study, and others, are being carried out in order to establish a Forensic Anthropology databank on age estimation and sex determination of skeletonized remains in Ghana. An osteometric study of sexual dimorphism in the sternal end of the right fourth rib on 346 consecutive coroner's autopsy cases (221 males, 125 females) of known age, sex, and race was conducted. The height and width of the sternal end of the rib were measured in each case. The sample was analyzed in three groups: young (< 30 years), old (> or = 30 years), and total sample (total group). Stepwise discriminant function analysis showed that the accuracy of sex determination varied from 80% in the young and 74% in the old groups to 78% for the total group. Statistical analysis of the results obtained when the functions derived from the study were tested using another batch of ribs showed the functions to be effective and reliable in determining sex. When functions derived from a previous study of American Whites were used to determine sex in our study sample, the vast majority of males were misclassified as females. This is the first time, to our knowledge, that a Black African population has been studied osteometrically to evaluate sexual dimorphism in the sternal end of the fourth rib.