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3.1 Overview of examination methods Forensic anthropological analyses involve the application of various examination methods and techniques. Those applied in any particular case are largely dependent on the question being asked, such as: Are the bones human? To whom do the skeletal remains belong? How long have the remains been here? How did the individual die? The amount and condition of skeletal material present also affects which methods are possible or most appropriate to apply. Forensic anthropologists can rarely provide definitive answers regarding interpretations of skeletal remains; all methods have inherent limitations (due to, for example, overlap between different biological groups or inherent limits of the observations or techniques). Common approaches used to make forensic anthropological conclusions about skeletal remains include macroscopic (visual) analysis, metric analysis, and radiology. In some cases, other specialized techniques or analyses such as histology or elemental analysis may also be employed. These analyses should be performed in a forensic anthropology laboratory which has access to some basic examination equipment (Figure 3.1). This should include at least one table large enough to lay out an entire adult skeleton in anatomical position. Large tables are useful for photographing the remains as well as providing a visual inventory. Ideally, the laboratory should be equipped with multiple tables, especially if more than one case is likely to be examined simultaneously. Since many cases are received with adhering soft tissue that may need to be removed (see Chapter 7), the laboratory should have a processing area with a water source and fume hood as well as any necessary processing tools (such as hotplates, crock pots, scalpels, forceps, and scissors). The laboratory should also be equipped with necessary safety supplies (such as gloves and lab coats) and must be capable of handling and managing biohazardous waste (Warren et al., 2008). In order to perform skeletal examinations, it is necessary to have at least a low-power microscope, measurement tools, and media for recording notes (such as paper or a computer). The laboratory examination area should also have sufficient overhead lighting as well as smaller hand-held light sources for directed lighting. For certain analyses, specialized analytical equipment or instruments may be required. The laboratory should also have enough storage for supplies, chemicals, reference materials, case files, and inactive cases (such as those awaiting additional examination). Areas where evidence is examined or stored must be secured, meaning that there is restricted access limited to analysts involved in the case. Forensic Anthropology. https://doi.org/10.1016/B978-0-12-815734-3.00003-8 # 2019 Elsevier Inc. All rights reserved.

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FIGURE 3.1 Forensic anthropology laboratory. Image courtesy of JPAC/CIL.

Anthropologists have developed and published many different methods for examining the human skeleton. As a result, there are usually multiple methods that can be used to estimate any particular parameter from human skeletal remains. Not all methods are equivalent, however; each has its own biases, error rates, conditions under which it is applicable, and required knowledge and equipment. These factors must be considered when choosing which method is most applicable for a particular case. Specific requirements for particular examination and documentation methods are discussed in the following sections.

3.2 Macroscopic analysis Virtually every anthropological examination involves some form of macroscopic or visual analysis. Macroscopic analysis is used in conducting an inventory of the remains, assessing the overall condition of the material, describing taphonomic changes, estimating sex, age, and ancestry, and interpreting pathology and trauma. Many conclusions can be drawn based on macroscopic analysis alone, including determining whether bones are human or nonhuman, and estimating the sex, ancestry, or age of the individual. Macroscopic analyses should be performed using sufficient ambient or overhead lighting and may also be aided by small light sources that can be used to view inside the cranium. Many macroscopic approaches, especially those relating to estimating aspects of the biological profile (see Chapters 8–10), involve assessing the presence or absence, degree of expression, or overall morphology of skeletal features. Such observations are often scored in some manner or compared to charts or exemplars such as photographs or cast exemplars. Many traits analyzed in this way are called morphoscopic traits (Ousley and Hefner, 2005). For example, in the assessment of sex, the pelvis may be examined for the presence or absence of a preauricular sulcus. In the assessment of ancestry, the anterior nasal spine may

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be categorized as slight, intermediate, or marked. In the estimation of age, the morphology of the pubic symphysis can be compared to written descriptions and exemplar casts to determine which of the described phases it most closely resembles. Morphoscopic features are sometimes referred to as nonmetric traits since they are visually assessed versus measured, but some practitioners use the term “nonmetric trait” only for those morphological features which are nonpathological, that can be scored as present or absent, such as the presence of a metopic suture (Buikstra and Ubelaker, 1994; Hefner et al., 2012). While macroscopic analysis has many advantages including ease of application and no need for sophisticated equipment, it also has limitations. It is typically considered more subjective, less standardized, and more prone to bias than some other types of analysis, such as metric analysis (Hefner, 2009) or examinations involving analytical instrumentation. By their nature, macroscopic interpretations are often less amenable to error analysis and sometimes rely heavily upon experience and training. Nonetheless, macroscopic approaches can be highly reliable and valid, and in some cases may be the only means of analysis possible. More recently, new statistical frameworks developed for morphoscopic and nonmetric trait data have been used to weight different skeletal features, providing more objective and robust approaches for estimating sex, ancestry, and age.

3.3 Metric analysis Metric analysis in forensic anthropological cases involves recording and analyzing skeletal measurements, also referred to as osteometrics. Metric analysis can often help to reveal skeletal differences that are difficult to detect and interpret by macroscopic methods alone, such as differences in size between males and females, and differences in cranial shape between ancestral groups. Measurements are also used in the calculation of certain parameters such as stature. Some advantages of metric analyses are that they add statistical weight to estimates and eliminate certain errors associated with more observational methods. Although fairly straightforward in most cases, metric analysis requires knowledge and training in the use of measurement instrumentation, locating particular landmarks on the remains, performing the relevant calculations, and interpreting the results. Sliding calipers, spreading calipers, osteometric boards, and measuring tapes (Figure 3.2) are the foundation for most metric analyses in forensic anthropology. Calipers and osteometric boards are used to take two-dimensional, linear skeletal measurements. Calipers measure from one specific point on a bone to another, while the osteometric board is used to measure the maximum lengths or breadths of long bones or to take other larger measurements which would exceed the maximum measuring capacity for standard calipers. A mandibulometer is used for taking linear and angular measurements of the mandible. Measuring tapes are typically used for measuring bone circumferences. Other methods for quantifying human remains, bony features, and human variation exist, including digitizers (Figure 3.3), laser scanners, and radiographic techniques, some of which can take measurements in three-dimensional space. Calipers and osteometric boards, however, are still the standard because of their wide availability, relatively low cost, and ease of use. While some measurements are very specialized and tailored to particular types of analyses, many forensic anthropologists employ some or all of a suite of relatively standardized skeletal measurements. Many of these measurements, especially those of the skull, are taken from a set of specified osteometric landmarks; those located on the skull are called craniometric landmarks. A list of these landmarks for the cranium can be found in Table 3.1, with their locations depicted in Figure 3.4. The standard measurements of the cranium and mandible are described in Table 3.2 and Figure 3.5. Abbreviations used in the measurements refer to the landmarks involved (displayed in lower case),

FIGURE 3.2 Instruments used to measure skeletal remains: (a) sliding calipers, (b) spreading calipers, (c) mandibulometer, (d) osteometric board, and (e) measuring tape.

FIGURE 3.3 Dr. Kate Spradley uses a 3-D digitizer to measure a cranium. Image courtesy of Texas State University.

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Table 3.1 Craniometric landmarks Landmark (and abbreviation) Alare (al) Alvelon (alv) Auriculare (au) Basion (ba) Bregma (b) Condylon (cdl) Dacryon (d) Ectoconchion (ec) Ectomolare (ecm) Euryon (eu) Frontomalare temporale (fmt) Frontotemporale (ft) Glabella (g) Gnathion (gn) Gonion (go) Infradentale (id) Lambda (l) Nasion (n) Nasospinale (ns) Opisthocranion (op) Opisthion (o) Prosthion (pr)

Zygion (zy)

Definition The most laterally positioned point on the anterior margin of the nasal aperture The point where the midline of the palate is intersected by a straight tangent connecting the posterior borders of the alveolar crests A point on the lateral aspect of the root of the zygomatic process at the deepest incurvature, wherever it may be The point where the anterior margin of the foramen magnum is intersected by the midsagittal plane The point where the sagittal and coronal sutures meet The most lateral points of the mandibular condyles The point on the medial border of the orbit at which the frontal, lacrimal, and maxilla intersect The intersection of the most anterior surface of the lateral border of the orbit and a line bisecting the orbit along its long axis The most lateral point on the lateral surface of the alveolar crest The most laterally positioned point on the side of the braincase The most laterally positioned point on the frontomalar suture A point located generally forward and inward on the superior temporal line directly above the zygomatic process of the frontal bone The most forwardly projecting point in the midsagittal plane at the lower margin of the frontal bone, which lies above the nasal root and between the superciliary arches The lowest point on the inferior margin of the mandibular body in the midsagittal plane The point on the mandible where the inferior margin of the mandibular corpus and the posterior margin of the ramus meet The point between the lower incisor teeth where the anterior margins of the alveolar processes are intersected by the midsagittal plane The point where the two branches of the lambdoidal suture meet with the sagittal suture The point of intersection of the nasofrontal suture and the midsagittal plane The lowest point on the inferior margin of the nasal aperture as projected in the midsagittal plane The most posteriorly protruding point on the back of the braincase, located in the midsagittal plane The point at which the midsagittal plane intersects the posterior margin of the foramen magnum The most anterior point on the alveolar border of the maxilla between the central incisors in the midsagittal plane; note that this point is anteriorly located on the alveolar process for measurements 6 and 8, and inferiorly located for measurement 10 The most laterally positioned point on the zygomatic arches

Modified from Moore-Jansen et al., 1994.

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FIGURE 3.4 Craniometric landmarks shown in (a) anterior, (b) lateral, and (c) inferior views. From Moore-Jansen et al., 1994.

FIGURE 3.4—cont’d

Table 3.2 Measurements of the cranium and mandible Measurement (and abbreviations) 1. Maximum Cranial Length (g-op, GOL) 2. Maximum Cranial Breadth (eu-eu, XCB) 3. Bizygomtic Breadth (zy-zy, ZYB) 4. Basion-Bregma Height (ba-b, BBH) 5. Cranial Base Length (ba-n, NL) 6. Basion-Prosthion Length (bapr, BPL) 7. Maxillo-Alveolar Breadth (ecm-ecm, MAB) 8. Maxillo-Alveolar Length (pravl, MAL) 9. Biauricular Breadth (ra-ra, AUB) 10. Upper Facial Height (n-pr,)

Definition The distance of glabella (g) from opisthocranion (op) in the midsagittal plane measured in a straight line The maximum width of the cranial vault perpendicular to the midsagittal plane wherever it is located The maximum breadth across the zygomatic arches, perpendicular to the midsagittal plane The direct distance from the lowest point on the anterior margin of the foramen magnum, basion (ba), to bregma The direct distance from nasion (n) to basion (ba) The direct distance from basion (ba) to prosthion (pr) The maximum breadth across the alveolar borders of the maxilla measured on the lateral surfaces at the location of the second maxillary molars The direct distance from prosthion to alveolon (alv) The least exterior breadth across the roots of the zygomatic processes, wherever found The distance from nasion (n) to prosthion (pr) Continued

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Table 3.2 Measurements of the cranium and mandible—cont’d Measurement (and abbreviations) 11. Minimum Frontal Breadth (ft-ft, WFB) 12. Upper Facial Breadth (fmtfmt) 13. Nasal Height (n-ns, NLH) 14. Nasal Breadth (al-al, NLB) 15. Orbital Breadth (d-ec, OBB) 16. Orbital Height (OBH) 17. Biorbital Breadth (ec-ec, EKB) 18. Interorbital Breadth (d-d, DKB) 19. Frontal Chord (n-b, FRC) 20. Parietal Chord (b-l, PAC) 21. Occipital Chord (l-o, OCC) 22. Foramen Magnum Length (ba-o, FOL) 23. Foramen Magnum Breadth (FOB) 24. Mastoid Height (p-m, MDH) 25. Chin Height (id-gn) 26. Height of Mandibular Body 27. Breadth of Mandibular Body 28. Bigonial Width (go-go) 29. Bicondylar Breadth (cdlcdl) 30. Minimum Ramus Breadth 31. Maximum Ramus Breadth 32. Maximum Ramus Height (mandibulometer needed) 33. Mandibular Length (mandibulometer needed) 34. Mandibular Angle (mandibulometer needed)

Definition The direct distance between the left and right frontotemporale The direct distance between the two frontomalare temporalia The direct distance from nasion (n) to the lowest point on the border of the nasal aperture on either side (ns) The maximum breadth of the nasal aperture The distance from dacryon (d) to ectoconchion (ec) The direct distance between the superior and inferior orbital margins perpendicular to orbital breadth The distance from left to right ectoconchion (ec) The direct distance between right and left dacryon The The The The

distance distance distance distance

from nasion (n) to bregma (b) taken in the midsagittal plane from bregma (b) to lambda (l) taken in the midsagittal plane from lambda (l) to opisthion (o) taken in the midsagittal plane of basion (b) from opisthion (o) taken in the midsagittal plane

The distance between the lateral margins of the foramen magnum at the point of greatest lateral curvature The projection of the mastoid process below, and perpendicular to, the eye-ear plane in the vertical plane The distance from infradentale (id) to gnathion (gn) The distance from the alveolar process to the inferior border of the mandible perpendicular to the base at the level of the mental foramen The maximum breadth measured in the region of the mental foramen perpendicular to the long axis of the mandibular body The distance between both gonia (go) The distance between the most lateral points on the two condyles (cdl) The minimum breadth of the mandibular ramus measured perpendicular to the height of the ramus The distance between the most anterior point on the mandibular ramus and line connecting the most posterior point on the condyle and the angle of the jaw The distance from the highest point on the mandibular condyle to gonion The distance of the anterior margin of the chin from a center point on a projected straight line placed along the posterior border of the two mandibular angles The angle formed by the inferior border of the corpus and the posterior border of the ramus

Modified from Moore-Jansen et al., 1994.

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16

FIGURE 3.5 Measurements of the cranium and mandible. From Moore-Jansen et al., 1994.

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or the abbreviated measurement (displayed in upper case). Standard measurements for postcranial elements are shown in Table 3.3 and Figure 3.6. Many guides, including Data Collection Procedures for Forensic Skeletal Material (Langley et al., 2016; Moore-Jansen et al., 1994) and Standards for Data Collection from Human Skeletal Remains (Buikstra and Ubelaker, 2004), offer more detailed definitions, considerations, additional measurements, and recommendations for which instruments are most appropriate for each measurement. It is recommended that this suite of standard measurements be recorded in all applicable cases since these are the most widely used measurements and have the greatest utility. There are also measurements of dentition which can be used for ancestry estimation and are discussed in more detail in Chapter 9. Table 3.3 Measurements of the postcranial skeleton Measurement

Definition

35. Maximum Length of Clavicle 36. Sagittal Diameter of the Clavicle at Midshaft 37.Vertical Diameter of the Clavicle at Midshaft 38. Height of the Scapula

The maximum distance between the most extreme ends of the clavicle The anterioposterior distance from the surface of the midshaft

39. Breadth of the Scapula

40. Maximum Length of the Humerus 41. Epicondylar Breadth of the Humerus 42. Maximum Vertical Diameter of the Head of the Humerus 43. Maximum Diameter of the Humerus at Midshaft 44. Minimum Diameter of the Humerus at Midshaft 45. Maximum Length of the Radius

46. Sagittal Diameter of the Radius at Midshaft 47. Transverse Diameter of the Radius at Midshaft 48. Maximum Length of the Ulna 49. Dorso-Volar Diameter of the Ulna 50. Transverse Diameter of the Ulna

The distance from the cranial to the caudal surface of the midshaft The direct distance from the most superior point of the cranial angle to the most inferior point on the caudal angle The distance from the midpoint on the dorsal border of the glenoid fossa to midway between the two ridges of the scapular spine on the vertebral border The direct distance from the most superior point on the head of the humerus to the most inferior point on the trochlea The distance of the most laterally protruding point on the lateral epicondyle from the corresponding projection of the medial epicondyle The direct distance between the most superior and inferior points on the border of the articular surface The maximum diameter that can be found at the humeral midshaft The minimum diameter that can be found at the humeral midshaft The distance from the most proximally positioned point on the head of the radius to the tip of the styloid process without regard to the long axis of the bone The anterioposterior diameter of the midshaft The distance between the maximum medial and lateral bone surfaces at the midshaft The distance between the most superior point on the olecranon and the most inferior point on the styloid process The maximum diameter of the diaphysis where the crest exhibits the greatest development The diameter measured perpendicular to the Dorso-Volar diameter at the level of greatest crest development

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Table 3.3 Measurements of the postcranial skeleton—cont’d Measurement

Definition

51. Physiological Length of the Ulna

The distance between the deepest point on the surface of the coronoid process and the lowest point on the inferior surface of the distal head of the ulna The least circumference near the distal end of the bone

52. Minimum Circumference of the Ulna 53. Anterior Height of the Sacrum

54. Anterior Breadth of the Sacrum 55. Transverse Diameter of the Sacral Segment 1 56. Height of the Innominate 57. Iliac Breadth 58. Pubis Length 59. Ischium Length 60. Maximum Length of the Femur

61. Bicondylar Length of the Femur 62. Epicondylar Breadth of the Femur 63. Maximum Diameter of the Femoral Head 64. Anterioposterior Subtrochanteric Diameter of the Femur 65. Transverse Subtrochanteric Diameter of the Femur 66. Anterioposterior Diameter of the Femur at Midshaft 67. Transverse Diameter of the Femur at Midshaft 68. Circumference of the Femur at Midshaft 69. Length of the Tibia

The distance from a point on the promontory in the midsagittal plane to a point on the anterior border of the tip of the sacrum measured in the midsagittal plane The maximum transverse breadth of the sacrum at the level of the anterior projection of the auricular surfaces The distance between the two most lateral points on the superior articular surface measured perpendicular to the midsagittal plane The distance from the most superior point on the iliac crest to the most inferior point on the ischial tuberosity The distance from the anterior superior iliac spine to the posterior superior iliac spine This distance from the point in the acetabulum where the three elements of the innominate meet to the upper end of the pubic symphysis The distance from the point in the acetabulum where the three elements forming the innominate meet to the deepest point on the ischial tuberosity The distance from the most superior point on the head of the femur to the most inferior point on the distal condyles, located by raising the bone up and down and shifting sideways until the maximum length is obtained The distance from the most superior point on the head of the femur to a plane drawn along the inferior surfaces of the distal condyles The distance between the two most laterally projecting points on the epicondyles The maximum diameter of the femur head measured on the border of the articular surface The anterioposterior diameter of the proximal end of the diaphysis measured perpendicular to the transverse diameter at the point of the greatest lateral expansion of the femur below the lesser trochanter The transverse diameter of the proximal portion of the diaphysis at the point of its greatest lateral expansion below the base of the lesser trochanter The anterioposterior diameter measured approximately at the midpoint of the diaphysis, at the highest elevation of the linea aspera The distance between the medial and lateral margins of the femur from one another measured perpendicular to and at the same level as the sagittal diameter The circumference measured at the midshaft at the same level of the sagittal and transverse diameters The distance from the superior articular surface of the lateral condyle of the tibia to the tip of the medial malleolus Continued

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Table 3.3 Measurements of the postcranial skeleton—cont’d Measurement

Definition

70. Maximum Epiphyseal Breadth of the Proximal Tibia 71. Epiphyseal Breadth of the Distal Tibia 72. Maximum Diameter of the Tibia at the Nutrient Foramen 73. Transverse Diameter of the Tibia at the Nutrient Foramen 74. Circumference of the Tibia at the Nutrient Foramen 75. Maximum Length of the Fibula

The maximum distance between the two most laterally projecting points on the medial and lateral condyles of the proximal epiphysis The distance between the most medial point on the medial malleolus and the lateral surface of the distal epiphysis The maximum distance between the anterior crest and the posterior surface at the level of the nutrient foramen The straight line distance from the medial margin to the interosseous crest, perpendicular to # 72 The circumference measured at the level of the nutrient foramen

76. Maximum Diameter of the Fibula at Midshaft 77. Maximum Length of the Calcaneus

78. Middle Breadth of the Calcaneus

The maximum distance between the most superior point on the fibular head and the most inferior point on the lateral malleolus The maximum diameter at the midshaft The distance between the most posteriorly projecting point on the tuberosity and the most anterior point on the superior margin of the articular facet for the cuboid measured in the sagittal plane and projected onto the underlying surface The distance between the most laterally projecting point on the dorsal articular facet and the most medial point on the sustentaculum tali

Modified from Moore-Jansen et al., 1994.

3.4 Fordisc In the 1990s, the procedure for performing discriminant function analysis was considerably simplified and statistically augmented by the development of Fordisc Personal Computer Forensic Discriminant Functions (or more commonly, simply “Fordisc”), an interactive computer program that calculates custom discriminant function analyses ( Jantz and Ousley, 2005). Fordisc is built on a large database of individuals of known sex and ancestry including the Howells data set (Howells, 1973; Howells, 1989) and a continuously growing Forensic Anthropology Data Bank ( Jantz and Moore-Jansen, 1988) (see Box 3.1). Unlike previous discriminant function approaches, Fordisc performs automated (as opposed to manual) statistical calculations, and can provide classifications based on any combination of standard measurements (as opposed to needing certain measurements to be available). The standard measurements described in the previous tables and figures were recently updated and are included in Fordisc and the Forensic Anthropology Data Bank. Forensic anthropologists are permitted and encouraged to submit measurements and biological profile information on their identified remains cases to the Forensic Data Bank, which increases sample sizes for the various reference samples available in Fordisc. It is important to note that while Fordisc will always provide a classification, there is significant responsibility on the user to properly understand and interpret the Fordisc output. The data must be properly collected and entered, the program must be correctly run, and the results must be appropriately interpreted. A background in statistical analysis, especially multivariate statistics, is essential for proper understanding of the software and the data output.

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35 39

36 38

37

40

41 42 45 46 47

51

49

50

52 48

56

54

58 55 57

53

59

61 65

67 62

64

66

68

63 60 72 71

70 74

73

69 75

76 78

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FIGURE 3.6 Measurements of the postcranial skeleton. From Moore-Jansen et al., 1994.

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BOX 3.1 THE FORENSIC ANTHROPOLOGY DATA BANK (FDB) Many forensic anthropological methods are based on studies of known reference material (i.e., skeletons of individuals of known sex, age, stature, and ancestry). Most skeletal collections available for study (at least within the United States) are composed largely of individuals born in the 19th century. These older skeletal collections are not the most appropriate reference sample for modern forensic casework, however, since they may not resemble modern populations due to secular changes in size, morphology, and proportions. The Forensic Anthropology Data Bank (FDB) was developed in 1986 due largely to the efforts of Dr. Richard Jantz, with the assistance of the National Institute of Justice, as a repository of data collected from modern known skeletons. Today, data are contributed by forensic anthropology practitioners, and have grown to include skeletal information on more than 3400 individuals. The skeletal information submitted for cases includes cranial and postcranial measurements, scores for various aging methods, nonmetric cranial information, details of trauma, congenital traits, and dental observations. In some cases, the FDB also contains demographic information such as place of birth, medical history, occupation, stature, and weight (Ousley and Jantz, 1998).

When using Fordisc, the measurements are recorded and entered into an electronic form, and then a series of skeletal populations to be included in the discriminant function analysis is selected (Ousley and Jantz, 2012) (Figure 3.7). After selecting the “Process” button, Fordisc uses linear discriminant function analysis to classify group membership by maximizing between-group differences using the sum of the numerical weights (i.e., factor) calculated for each measurement (Ousley and Jantz, 2012). These factors enable the classification of unknown skeletons, provided that the unknown individual belongs to a group represented in the reference samples. This is an important point, because Fordisc will always classify the measurements of the skeleton into the closest selected group, even if the individual belongs to a group that is not selected (or may not even exist within the reference database). Interpretation of the results is therefore critical and is described in the following in more detail. Fordisc uses Mahalanobis D2, a multivariate measure of the difference between groups, to measure the average differences between groups for each analysis. Fordisc’s output provides the D2 values (labeled as “Distance from”) for the unknown set of measurements relative to all groups used in the analysis, with the smallest D2 value representing the group most similar to the measurements of the unknown skeleton (Figure 3.8). The unknown individual will always be classified into the population with the smallest Mahalanobis distance. In some instances, a few of the selected populations will have very similar Mahalanobis distances, requiring close examination by the analyst to interpret the results. Next in the output is the posterior probability value, which provides a measure of the relative distance of the unknown skeleton to each group, compared to the other groups selected for comparison. Note that all posterior probabilities will always sum to 1.0 (with the probabilities ranked from highest to lowest for each group included in the analysis), and that the unknown skeleton will be assigned to one of the groups selected (the group with the smallest Mahalanobis distance, which is typically also the group with the highest posterior probability). Groups with posterior probabilities less than 0.1 can usually be excluded from the analysis. After posterior probability are three typicality probabilities (labeled as “Typ F,” “Typ Chi,” and “Typ R”), these measure the absolute distance of the unknown skeleton to each group centroid, or how “typical” the skeleton is for each group (Figure 3.9). High typicality values suggest that the skeleton is similar to the other skeletons in that reference group, while low values suggest that it is atypical. Groups with typicality probabilities less than 0.01 can usually be excluded from

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FIGURE 3.7 Fordisc electronic forms. From Jantz and Ousley, 2005.

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FIGURE 3.8 Fordisc ancestry results for a white female skull. Note that the posterior probability of 0.990 indicates that the skull is more similar to White Females than any of the other groups selected, and the typicality of 0.915 indicates that the skull is highly typical of other White Female skulls. From Jantz and Ousley, 2005.

FIGURE 3.9 Posterior probabilities and typicalities. Modified from Ousley and Jantz, 2012.

the analysis, although measurements should be checked for errors. Fordisc also generates two- and three-dimensional graphical representations of the results, which can assist the analyst in interpretation (Figure 3.10). The differences between the three typicality measures are small but each typicality measure will produce different results. The “Typ F” is a typicality based on the F distribution, which accounts for the Mahalanobis distance and sample size of a group; this measurement can be affected by overfitting the data, resulting in higher than normal typicality probabilities. The “Typ Chi” is based on the chi-squared distribution of the Mahalanobis distances only; this measurement is not affected by sample size and usually provides lower typicality values than the “Type F.” The “Typ R” is a typicality based on the ranked Mahalanobis distances of each individual and the unknown in a group; this

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4.0 X

2.0 Can 2 (33.4%)

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0.0

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HF JF AF

–2.0

–2.0

0.0 Can 1 (41.6%)

2.0

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FIGURE 3.10 Fordisc graph of canonical variates analysis of an unknown female skull. The “X” denotes the unknown individual, which falls within the ellipse of the White Female (WF) group and outside of the ellipses for the other selected groups. From Jantz and Ousley, 2005.

FIGURE 3.11 Flowchart for using Fordisc. Modified from Ousley and Jantz, 2012.

measurement is more subjective than the other typicalities and requires larger sample sizes in order to provide meaningful interpretations ( Jantz and Ousley, 2005). Fordisc analyses can be run initially by choosing to include all measurements and all groups (Figure 3.11). Fordisc will notify the user if any measurements are especially atypical (too large or too small), which may be the result of measurement or recording errors that can be caught and fixed early in the analysis. Analyses should be repeated, typically eliminating groups with posterior probabilities of less than 0.1 and typicality probabilities of less than 0.01. Analyses ideally result in two to four remaining classification groups. The user should also ensure that all selected populations have

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large enough samples based on the number of variables selected. If the sample sizes are too small, a large number of variables will overfit the model, resulting in potential misclassifications. A general rule is to have one variable (measurement) for every three individuals in the smallest population; for example, in an analysis with multiple populations where the smallest population has a sample size of 45, the maximum number of variables should be 15. Overfitting can be avoided using the stepwise variable selection (available under “Options”) and/or by removing measurements. Fordisc’s primary reference samples are based on modern human skeletons and thus are not appropriate for classifying archaeological material (Ousley et al., 2009). Fordisc does, however, include W. W. Howells’ craniometric database, consisting of measurements of historic and prehistoric crania from various parts of the world (Ousley and Jantz, 2012). This may be applicable for comparisons with historic or prehistoric skulls for remains which may be of questionable medicolegal significance, but should be used cautiously due to the large number of groups represented. Specific applications of Fordisc can be found in this text in the chapters on sex estimation (Chapter 8), ancestry estimation (Chapter 9), and stature estimation (Chapter 11).

3.5 Statistics, error, and uncertainty in forensic anthropology Skeletal measurements can be analyzed and interpreted using statistics much more readily than most macroscopic methods, and the use of statistical analysis in conjunction with qualitative descriptions in forensic anthropological casework is recommended. In order to select and apply appropriate statistical models in casework and research, it is important that forensic anthropologists have a strong background in statistics and quantitative methods of data analysis. Definitions of various basic statistical terms that are commonly used in forensic anthropological analyses can be found in Table 3.4. Two of the more commonly employed statistical analyses in forensic anthropology are regression analysis and discriminant function analysis. Regression analysis is a statistical approach that assesses the relationship (i.e., correlation) between two or more variables. The simplest form of regression analysis is a linear, bivariate (two-variable) regression that describes the relationship between the two variables of interest. Such analyses are often used in forensic anthropology, for example when determining the relationship between the length of a bone and an individual’s known stature (see, for example, Figure 11.3). This mathematical relationship then allows for the estimation of an unknown stature based on a known bone length (or vice versa). Discriminant function analysis is a statistical approach that is used to predict membership to a group based on a set of variables. In forensic anthropology, this type of analysis is often used to estimate ancestry (where the “groups” are, for example, European, African, and Asian ancestry) and sex (where the “groups” are male and female sex) based on a series of cranial and postcranial measurements. Discriminant function analysis proceeds by inserting the appropriate measurements into discriminant function equations and assessing where the resulting calculation falls with respect to various sectioning points, which are developed based on a reference sample of individuals of known group membership. Error can be defined in a number of ways, including deviation from what is correct, having false knowledge, a mistake, or the difference between an observed value or measurement and the true value. Error can result from a number of different causes in forensic science, and the concept is often vague and subject to a variety of interpretations (Christensen et al., 2014). There are several general categories

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Table 3.4 Basic statistical terms Term

Mean Median

Mode Variance Standard Deviation Range Standard Error

Error Accuracy Precision Reliability Validity Bias

Definition Measures of Central Tendency The arithmetic average of all values A numerical value that separates the lower half from the upper half of the distribution; for an odd number of values, it is the middle value; for an even number of values, it is the mean of the two middle values The most common value represented in a data set Measures of Variation A measure of the spread of values in a data set A measure of how much variation exists in a range of values, expressed in the same unit of measurement as the mean The difference between the highest and lowest value of a given set of values The standard deviation of a distribution of samples, used to measure uncertainty of the true population mean and standard deviation Measures of Sources of Error The difference between an estimated quantity and its true value The degree of closeness of a measurement to the true value How close different measurements are to each other, usually measured by the standard deviation of the estimator and known as the standard error The ability to obtain the same result using the same methods and instrument The degree to which an observation or result reflects empirical reality A systematic (not random) deviation from the true value

of error (Christensen et al., 2014; Dror and Charlton, 2006), which are discussed further in the following paragraphs. Practitioner error refers to human error or mistakes. Practitioner errors may be unintentional and related to negligence or incompetence, such as blunders like transposing numbers when recording data, incorrect instrument use, selection of inappropriate methods, or improper method application. In forensic anthropology, this might include incorrectly transcribing measurements or performing calculations, or selection of a particular age estimation method when another might be more appropriate. Practitioner error may also be intentional, such as fraudulent behavior (i.e., misconduct). Practitioner error can be reduced through quality assurance systems, training, proficiency testing, peer review, and adhering to validated protocols and discipline best practices (Christensen et al., 2014; Dror and Charlton, 2006). Instrument (or technological) error is the difference between an indicated instrument value and the actual (true) value. Some acceptable amount of instrument error is generally recognized to exist (which has typically been determined by the instrument’s manufacturer), but can be minimized largely by proper maintenance and calibration of instruments (Christensen et al., 2014; Dror and Charlton, 2006). Instruments used in forensic anthropology may include measurement tools such as calipers and osteometric boards, analytical instruments such as XRF and XRD, and diagnostic equipment such as radiology devices. All should be maintained properly and calibrated regularly to minimize instrument error.

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Statistical error refers to random variation or deviation from actual and predicted values. This “error,” which often merely expresses normal variability, is inherent in measurements and estimates because they are based on the properties of a sample (Christensen et al., 2014). In forensic anthropology, this may be seen in calculations such as stature estimation. Regression formulae are based on the characteristics of a large sample which may or may not have the exact same properties as the case at hand; this is why these estimations are best expressed as intervals rather than point estimates. Technique (or methodological) error relates to inherent limitations of a method (Christensen et al., 2014; Dror and Charlton, 2006). Method limitations in forensic anthropology are often a function of how measurements or traits overlap among different groups or to the frequency of the observed trait(s) in the population at large. These limitations are not themselves “errors”; they are a function of the sensitivity or resolving power of the method that can result in an incorrect conclusion. For example, femoral head size may be used to estimate sex, but because there is some overlap between males and females (i.e., some males have smaller femoral heads, and some females have larger femoral heads), there is a chance that any given sex estimate based on femoral head size may be incorrect. There is no way to “minimize” these types of method limitations (with, for example, additional training or calibration)—they simply exist as a function of inherent limits in the material itself (in this case, inherent biological variation in femoral head size) (Box 3.2). Such limitations, however, should be acknowledged and communicated in reports and testimony. Moreover, the selection of good research designs and appropriate statistical models will assist in producing valid scientific methods with known or potential rates of error. Researchers in forensic anthropology are now using more sophisticated measurement techniques and statistical analyses to evaluate forensic evidence, and are also increasingly quantifying traits that had previously been difficult to address in this fashion. For the most part, contemporary anthropology research presents error values, but the term is often not defined and the potential effect on evidentiary examination is not addressed (Crowder and Ingvoldstad, 2009). In addition, anthropologists are increasingly engaging in measures to reduce error such as quality assurance programs and peer review. Forensic anthropologists must be concerned with clarity, reliability, and validity of methods, and should also be cognizant of the concerns of the legal community, which includes understanding how the courts view and evaluate scientific evidence. This can best be accomplished by understanding, acknowledging, and communicating method limitations and potential sources of error in research and forensic analyses.

BOX 3.2 “ZERO ERROR” Some forensic practitioners have claimed that the error rate for their technique or method is zero; see US v. Mitchell (1998) for one example. The following testimony was provided by a fingerprint examiner explaining the reasoning behind the zero error rate claim: “And we profess as fingerprint examiners that the rate of error is zero. And the reason we make that bold statement is because we know based on 100 years of research that everybody’s fingerprints are unique, and in nature it is never going to repeat itself again.” (People v. Gomez, 2002) What this expert fails to understand is that despite the strength of the basis for fingerprint association (that there is a low probability for two identical fingerprint patterns to exist), error and limitations still exist in the comparison methodology. Error depends not only on how rare a particular trait is, but also on how reliable and valid the methods are for determining whether two fingerprints may be associated to the same person. There is always a nonzero probability of error, and to claim an error rate of zero is inherently unscientific. Reasons behind such misunderstandings of error range from improper training in statistics and the scientific method to concerns that current methods will be exposed as lacking an empirical footing.

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BOX 3.3 GEOMETRIC MORPHOMETRICS Geometric morphometrics (GM) is an approach involving the multivariate (multiple-variable) statistical analysis of Cartesian coordinate data using landmark point locations, and is becoming widely used in forensic anthropology (Slice, 2007). This type of analysis preserves information about the relative spatial arrangement of data points such as cranial landmarks, allowing for visualization of group and individual differences. Typically, GM data are collected using a digitizer, which records three-dimensional point data (i.e., an x-, y-, and z-coordinate for each point), usually from a defined skeletal landmark (e.g., bregma, prosthion, basion, etc.). These data can then be used to analyze linear distances between the landmarks or overall shapes. While currently used primarily in research applications in the study of group and individual differences (e.g., Kimmerle et al., 2008), it may also be used as an analytical tool in forensic casework.

Geometric morphometric comparison of cranial landmarks from different populations. Image courtesy of Kate Spradley.

Another area that has seen increased scholarly attention in recent years is improved statistical analysis in forensic anthropological research and case analysis. Many of the traditional approaches as well as some of the current techniques used in forensic anthropology are relatively subjective, employing a combination of traditional scientific methodologies and less rigorous observational methodologies (Christensen and Crowder, 2009). This does not mean, however, that robust statistical approaches cannot be applied. In addition, Bayesian and other more complex statistical approaches as well as geometric morphometrics (Box 3.3) are increasingly being applied to anthropological problems.

3.6 Radiology Radiology is the study of high-energy radiation used to examine and diagnose internal structures. The process of using radiology to make images is called radiography. Radiology in forensic anthropology is useful for documentation as well as detection and diagnostic applications, and may include

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traditional 2-dimensional radiography or computed tomography (CT). It can be used to produce a record of the condition of the remains at the time of examination, detect the presence of foreign material such as a bullet (Figure 3.12), and visualize internal skeletal structures that are not visible to the naked eye such as paranasal sinuses or developing dentition. It can also be used to diagnose conditions such as antemortem fractures or pathological conditions, or to see the placement of surgical implants. Taking and examining radiographs requires some knowledge of the relative radiodensities of various materials. Keeping thickness as well as other technical parameters constant, the radiographic appearance of materials will vary as a function of their attenuation properties (Figure 3.13). This explains, for example, why it is possible to detect foreign material such as projectiles within bone using radiology—bullet lead attenuates more x-rays (i.e., appears more radiopaque) than bone, making it appear distinct from bone (which attenuates more x-rays than soft tissues but less than lead) in a radiologic image. The radiologic investigation of human remains began soon after the discovery of x-rays (see Box 3.4) as investigators came to realize that x-rays provided a nondestructive means of examining human remains. Today, the value of radiology is well established in criminal and medicolegal work, and it is considered to be a standard component of most forensic anthropological analyses. One advantage of radiology in the analysis of skeletal remains is that because there is no concern regarding health hazards of the decedent due to x-ray exposure, skeletal remains can be exposed to high amounts of radiation that would probably be considered unhealthy for live individuals. Not all forensic anthropologists have received formal training in radiology or the use of radiologic equipment, however, so collaboration with a radiologist or technician with experience in this area may be required. Although radiology units can be expensive, they have become commonplace in hospitals, morgues, and crime labs, and are therefore often accessible to a forensic anthropologist. The advent of digital radiography (versus film radiography) means that radiologic images can be viewed almost instantaneously, and the reduction in size and increase in portability of x-ray devices has

FIGURE 3.12 Radiograph showing fractured humerus and projectile fragments. Image courtesy of B.G. Brogdon, M.D.

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FIGURE 3.13 Radiographic appearance of various materials—left to right: ceramic, fossilized shell, nonhuman long bone fragment, plastic, human metacarpal. From Christensen and Passalacqua, 2018.

greatly facilitated the use of forensic radiology in the field (such as in mobile morgues used in mass fatality incidents). Imaging technology has also advanced in ways that improve visualization of skeletal structures as well as associated nonskeletal materials (Figure 3.14). Computed tomography (CT), for example, allows 3-dimensional reconstruction and volume rendering of skeletal structures (Figure 3.15), as well as visualization or even isolation of nonskeletal materials (Figure 3.16). This can be useful in analyses such as radiologic identification, assessing biological characteristics such as age and sex, diagnosing skeletal trauma and pathology, and detecting and locating foreign materials such as projectiles and their wound paths. While such assessments can also often be made from traditional 2-dimensional radiographs, visualization is significantly improved with CT in most cases, and because they are three dimensional, there is no concern for overlapping structures or discrepancies in projection angle which often complicate analysis of 2D images. Moreover, because CT is becoming very common in clinical diagnostics, CT images are increasingly available as antemortem records in radiologic identification comparisons. Data from CT scanning files can also be used to make 3D printed replicas of skeletal material (see Chapter 7).

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BOX 3.4 DISCOVERY OF X-RAYS On Friday afternoon, November 8, 1895, the German physicist Wilhelm Conrad Roentgen, working in his Worzburg physics laboratory, made a serendipitous and monumental discovery. When he filled a vacuum tube with a special gas and passed electric voltage through it, it produced a fluorescent glow, and Roentgen realized that a previously unknown ray (termed x-ray) was being emitted from the tube (Roentgen, 1895; English translation in Pais, 1986). Roentgen also reported that the materials containing atoms with a high atomic number (Z), notably lead, attenuated these rays much more readily than atoms with few protons in the nucleus such as hydrogen and many other atoms in soft tissues. One of the first medical photographs (the first roentgenogram or radiograph) is of the hand of Roentgen’s wife, made on December 22, 1895. As usual, she was wearing her wedding ring, and its image showed up clearly on the radiograph (see photo: Roentgen, 1895, and inset, radiograph of Frau Roentgen’s hand). For his discovery of x-rays, Roentgen received the first Nobel Prize in physics in 1901.

Image from: http://www.xtal.iqfr.csic.es/Cristalografia/parte_02-en.html (Accessed August 2012)

Postmortem CT can also reduce the need for dissection or processing in cases where remains are fresh or not completely skeletonized, and generally enhances postmortem examinations. A team of forensic pathology and radiology experts in Switzerland pioneered “Virtopsy,” a multidisciplinary approach to postmortem imaging (Virtopsy n.d.; Thali et al., 2003; Thali et al., 2009; Schweitzer et al., 2014). The technique involves the use of CT, MRI, angiography, optical 3D surface scanning, and 3D photogrammetry integrated into the “Virtobot” (Figure 3.17) to document forensic evidence in a minimally invasive and observer-independent manner. The approach minimizes and in some cases eliminates the need for a traditional autopsy.

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FIGURE 3.14 CT scan of a cranium showing frontal sinus, as well as foreign material (soil) in the right maxillary sinus. A tooth root with a broken missing crown is also noted in the position of the right lateral incisor. From Christensen et al., 2018.

FIGURE 3.15 Volume renderings of a CT scan showing frontal sinus in coronal (left) and axial (right) sections. From Christensen and Hatch, 2017.

Other alternate forms of CT are also available and may be used by forensic anthropologists in their analyses. Cone beam CT (or CBCT) is commonly used in maxillofacial clinical applications including intraoperative imaging. Compared to traditional CT, skeletal tissue resolution is generally improved with CBCT, and machines are smaller and therefore typically more portable and more affordable.

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FIGURE 3.16 CT scan of a mandible with associated wire (left); and wire isolated using CT scan postprocessing software (right). From Christensen et al., 2018.

FIGURE 3.17 The “Virtobot,” including CT scanner, robot arm, surface scanner, camera, and biopsy needles. Image courtesy of Zurich Institute of Forensic Medicine.

Because of their use in maxillofacial applications, the frontal and maxillary sinuses are often captured, which may be useful in identification comparisons (Figure 3.18). Industrial CT is currently used by very few forensic anthropology laboratories, though it offers a number of significant advantages (Christensen et al., 2018). For example, industrial CT is capable of higher dosages and longer scan times, which can allow greater resolution (Figure 3.19).

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FIGURE 3.18 CBCT used to examine paranasal sinuses. From Sarment and Christensen, 2014.

FIGURE 3.19 Top: Example of spatial resolution possible on a proximal femur; Bottom: Femur cross sections showing image resolution capable using an industrial CT scanner (left) versus a traditional medical CT scanner (right). From Christensen et al., 2018.

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3.7 Histology Histology is the study of the microscopic structure of tissues. A histological analysis of skeletal material can be used in forensic anthropological examinations to determine whether unknown material is bone, and whether or not the bone can be excluded as being human in origin (see Chapter 4). It can also be used in the assessment of skeletal age on the basis of bone remodeling (see Chapter 10). In addition, it can be useful in the diagnosis of disease or recognizing the early stages of bone healing (Barbian and Sledzik, 2008; Schenk, 2003) (see Chapter 13). Histological analysis requires some specialized equipment and training which may not be available in all forensic anthropology laboratories. In order to observe the microscopic structures of osseous tissue, the bone must be prepared as thin sections of around 50–100 μm thick. This is typically accomplished by cutting sections of the bone into  1 mm wafers using a sectioning saw (Figure 3.20), and then grinding and polishing the wafer until it is suitably thin for microscopic examination (Figure 3.21), which means that it must transmit light, and that there ideally are few if any overlapping structures when viewed on a mounted microscope slide (Figure 3.22). In some cases, particularly if bone fragments are very small or taphonomically compromised (e.g., burned, mineralized, or highly weathered), the bone may need to be embedded in resin to stabilize it during cutting (as shown in Figure 3.20). This requires additional supplies, such as the chemicals needed to prepare the resin as well as a vacuum pump to ensure that the resin completely penetrates the bone sample and that all air bubbles are removed.

FIGURE 3.20 Wafering saw being used to cut a resin-embedded bone fragment into thin sections for histological analysis. From Crowder et al., 2012.

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FIGURE 3.21 Grinder/polisher being used to further reduce the thickness of the bone section (bottom). From Crowder et al., 2012.

FIGURE 3.22 Bone section being mounted on a glass microscope slide. From Crowder et al., 2012.

The thin section is then mounted on a glass microscope slide and examined using light microscopy, sometimes with the aid of tissue staining and/or polarized light. Using this approach, the microstructure of the bone can be visualized, imaged, measured, and interpreted. Because histological examination is a destructive process, it should only be used when necessary and should follow thorough macroscopic and other nondestructive analyses.

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3.8 Elemental analysis Elemental analysis is the analysis of a material for its elemental or isotopic composition. In anthropological examinations, elemental analysis is useful in two particular areas. First, it may be used in the determination of whether a material is bone or some other material (see Chapter 4) based on whether or not it contains bone’s signature levels of calcium and phosphorus. This approach is especially useful when pieces of unknown (but suspected to be skeletal) material are very fragmented and/or taphonomically compromised (Christensen et al., 2012). This technique may also be used to determine whether bone (especially cremated bone) is mixed or contaminated with other material (Gilpin and Christensen, 2015). Elemental analysis may also be used in stable isotopic profiling of human tissues such as bones, teeth, hair, and fingernails as a means of identifying an individual’s likely dietary or residence pattern based on food and water consumed. Isotopes are variants of an element which share the same number of protons but differ in the number of neutrons. Stable isotopes are those isotopes which do not spontaneously decay over time (as compared to radioactive isotopes, which decay into other forms over time). Organisms incorporate different relative abundances of stable isotopes (e.g., 13 12 C/ C) into their tissues from food and drink consumed during life. In certain cases, stable isotope analysis can provide information on dietary patterns, such as whether an individual was vegan or had a diet that was high in corn (because corn is a plant that is enriched in the heavy isotope 13C). These analyses can be especially useful for unidentified decedents who are nonlocal to the area where they died. Stable isotope analysis, especially of incremental tissues such as teeth, hair, and nails, can also be used to track an individual’s migration history and residence patterns based on signatures that reflect a particular drinking water source or geological region where food is grown (Meier-Augenstein, 2006, 2010; Bartelink et al., 2013, 2016). Isoscapes are maps of predictions of isotope ratios (Figure 3.23). Comparison of an isotope profile of an individual’s tissues to these known distributions can suggest previous patterns of residence. For example, oxygen isotope values in teeth record the drinking water source at the time of tooth formation, whereas hair and nails provide a more recent record representing the last several months of life. This information can be particularly useful in cases where a body is recovered a significant distance from where the individual last resided. These applications can be used to predict possible regions of origin of unidentified migrants from the US/Mexico border as well as remains of soldiers who died in conflicts overseas. Elemental analysis requires the use of specialized equipment such as scanning electron microscopy/ energy dispersive spectroscopy (SEM/EDS), x-ray fluorescence spectrometry (XRF), or x-ray diffraction (XRD) (Figure 3.24). These instruments are quite expensive and require extensive training, and therefore elemental analysis is only performed in a few anthropology laboratories. This equipment, however, is generally available in analytical chemistry and biology laboratories, as well as in many major crime laboratories.

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FIGURE 3.23 Hydrogen (top) and oxygen (bottom) isoscape prediction maps based on tapwater in the contiguous US. Modified from Ehleringer et al., 2010.

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FIGURE 3.24 x-ray fluorescence spectrometer being used to analyze a possible bone fragment. Image courtesy of Thomas Lera, Smithsonian National Postal Museum.

3.9 Case study: Method selection and metrics Unidentified skeletal remains were submitted to a university forensic anthropology laboratory for analysis, including the estimation of a biological profile to help narrow the search for possible missing persons to whom the remains might belong. The skeleton was incomplete, consisting only of a cranium (mostly complete), a number of vertebrae, several ribs, incomplete long bones of the upper limbs, and complete right femur. Numerous methods have been developed and documented to estimate sex from various parts of the skeleton, including metric and morphoscopic analyses. While features of the pelvis have been shown to be most accurate for sex estimation (see Chapter 8), no bones from the pelvis were recovered in this case and therefore these methods could not be used. Studies have shown that metric analysis of postcranial bones results in greater classification accuracy for sex estimation than methods using the cranium (Spradley and Jantz, 2011). Moreover, the method’s validity is supported by statistical data and error rates. Therefore, measurements of the femur were used to estimate sex. The maximum femoral head diameter was measured at 48 mm (Figure 3.25), which more closely resembles average measurements of males versus females, with an 86% correct classification rate using a sectioning point of 44 mm for Black males, and an 88% correct classification rate using a sectioning point of 45 mm for White males. The remains were eventually identified as a 55-year-old European male based on dental records.

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FIGURE 3.25 Femoral head measurement method selected for sex estimation.

3.10 Case study: Radiology A newly hired high school anatomy teacher found a human mandible while cleaning out a storage area in preparation for class. All of the other teaching materials used at the school were plastic replicas, but this one appeared to be a real bone. The teacher was aware that certain real human bones can be used for teaching purposes, but uncertain about the origin of the bone and whether the school should have possession of it, he contacted the police. The bone was in good condition overall with the exception of some apparent staining and handling wear, likely from being used in class. The police sent the mandible to a forensic laboratory for analysis. A CT scan confirmed the presence of two dental restorations (Figure 3.26), which meant that it was likely fairly recent in origin. The tooth roots were all completely developed, indicating that the individual was likely greater than 18 years old. An impacted third molar was also present. A forensic odontologist charted the teeth for entry into NamUs, and a DNA sample was taken for entry into CODIS. The bone was not returned to the school and the case remains under investigation.

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FIGURE 3.26 CT scan of mandible showing dental restorations and impacted molar. From Christensen et al., 2018.

3.11 Summary •

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A variety of methods are used in skeletal analysis, including macroscopic (visual) observation, metric analysis, radiology, histology, and elemental analyses. The most appropriate method selected for a particular case depends on a number of factors including what is being asked and the type and amount of material present. In most cases, metric analysis and instrumental methods are more objective and more easily quantified than macroscopic methods. Statistical analysis forms the basis of many interpretations in forensic anthropology, including the biological profile and personal identification. Measures of central tendency and variation form the foundation of skeletal estimations based on metric data. Modern human skeletal samples, such as those represented in the Forensic Anthropology Data Bank, are essential for forensic casework. Changes in skeletal size, morphology, and proportions over time make it important to use modern reference samples when possible. Radiology is useful as a method of documentation, and is an essential tool for the analysis of trauma and pathology, and for assessing features that are useful for personal identification.

3.12 Test yourself •

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Discuss some of the advantages and disadvantages of macroscopic versus metric analysis. When should specialized destructive methods such as histology or elemental analysis be used? If you needed to perform destructive analysis, how would you justify this to law enforcement? Why is it important to have modern documented human skeletal collections available for study? How would using data from earlier collections possibly affect your results?

Definitions

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Describe the differences between statistical, practitioner, technique, and instrument error. Can you think of additional examples of each type of error that may be encountered in forensic anthropological analyses? Explain why no expert can claim that his or her error rate is zero. What information can be discovered through the use of radiology? How might this information be used in a court trial?

Definitions Attenuation The reduction in energy of a beam of radiation when passed through a material Bayesian Relating to statistical methods based on Bayes Theorem Cartesian A coordinate system that specifies the position of a point in space Computed tomography (CT) A radiologic imaging technique that combines many computer processed x-ray images to make cross-sectional images or slices Craniometric landmarks Osteometric landmarks applied to the skull Discriminant function analysis A statistical analysis used to predict category or group membership Elemental analysis The process of analyzing a material for its elemental and sometimes isotopic composition Error The difference between an estimated or observed value and the true value Histology The study of the microscopic structure of tissues Instrument error The difference between an indicated instrument value and the actual (true) value Isoscape A spatial prediction of elemental isotope ratios Isotope A variant of an element which shares the same number of protons, but differs in the number of neutrons; radioactive isotopes spontaneously decay over time while stable isotopes do not Light (or optical) microscopy The use of microscopes and transmitted light to observe structures that cannot be seen with the naked eye Macroscopic Of a size that is measurable, assessable, or visible with the naked eye Mahalanobis D2 A multivariate measure of the difference between groups Micrometer (or micron, μm) One-millionth of a meter (1  10–6 m); or one-thousandth of a millimeter (0.0001 mm) Morphoscopic trait A trait that is assessed based on presence or absence, degree of expression, or overall morphology Nonmetric trait Dichotomous, discontinuous, epigenetic skeletal variant that can be classified as present or absent (also called discrete trait) Osteometric landmarks A standardized set of skeletal locations from which measurements are taken Osteometrics The practice of recording and analyzing skeletal measurements Posterior probability In Fordisc, a measure of the relative similarity of an unknown skeleton to the groups selected for comparison Practitioner error Human error; mistake Radiodensity The relative ability of substances to resist the passage of radiant energy; those substances that are more resistant (attenuate more) are radiopaque while those that are less resistant (attenuate less) are radiolucent Radiography The use of radiology to make images (radiographs) Radiology The use of high-energy radiation (such as x-rays) in the imaging, examination, and study of internal structures, and in the diagnosis and treatment of disease Regression analysis A statistical analysis used to measure the relationship between two variables Secular change Temporal or long-term trends Statistics The science of collecting, organizing, and interpreting numerical data Statistical error Random variation or deviation from actual and predicted values, generally represented by the standard error or the statistical probability of error

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Chapter 3 Skeletal examination and documentation methods

Technique error Inherent limitations of a method or approach which are sources of potential error, often a function of how measurements or traits overlap among different groups or to the frequency of the observed trait(s) in the population at large Typicality In Fordisc, a measure of the absolute similarity of an unknown skeleton to the groups selected for comparison

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