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Post by Admin on Mar 10, 2018 18:34:43 GMT
Bone measurement analysis indicates that the remains found on a remote island in the South Pacific were likely those of legendary American pilot Amelia Earhart, according to a UT researcher. Richard Jantz, professor emeritus of anthropology and director emeritus of UT’s Forensic Anthropology Center, re-examined seven bone measurements conducted in 1940 by physician D. W. Hoodless. Hoodless had concluded that the bones belonged to a man. Jantz, using several modern quantitative techniques—including Fordisc, a computer program for estimating sex, ancestry, and stature from skeletal measurements—found that Hoodless had incorrectly determined the sex of the remains. The program, co-created by Jantz, is used by nearly every board-certified forensic anthropologist in the US and around the world. The data revealed that the bones have more similarity to Earhart than to 99 percent of individuals in a large reference sample. The new study is published in the journal Forensic Anthropology. Jantz also compared the bone lengths with Earhart’s. Her humerus and radius lengths were obtained from a photograph with a scalable object. The scale was provided by Jeff Glickman of Photek. Her tibia length was estimated from measurements of her clothing in the George Palmer Putnam Collection of Amelia Earhart Papers at Purdue University. A historic seamstress took the measurements, which included the inseam length and waist circumference of Earhart’s trousers. Based on this information, Jantz concludes that “until definitive evidence is presented that the remains are not those of Amelia Earhart, the most convincing argument is that they are hers.”
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Post by Admin on Mar 13, 2018 18:59:50 GMT
Hoodless’s Methods and the State of the Art in 1941 There are both general and specific reasons to question Hoodless’s analysis. These do not relate to his competence as much as they do to the state of forensic anthropology at the time. Forensic anthropology was not well developed in the early 20th century. There are many examples of erroneous assessments by anthropologists of the period. E. A. Hooton, one of the most prominent and influential biological anthropologists of the early to mid-20th century, had considerable difficulty sexing the skeletons from Pecos Pueblo, ending up with a sex ratio favoring males (Hooton 1930). Weisensee and Jantz (2010) and Tague (2010) have reexamined the Pecos collection and concluded that Hooton sexed too many females as males, likely because he gave the skull more weight than the pelvis in his sex assessments. G. K. Neumann is known for establishing a typological framework for Native American remains (Neumann 1952). In so doing he examined hundreds of crania from different parts of the United States. Yet when confronted with a cranium from Jamestown, clearly of African ancestry, he misidentified it as Native American (Neumann 1958), presumably because the archaeologist who excavated it thought it to be Native American (see Cotter 1958:24). Given the state of the art at the time, why should we suppose that Hoodless, who as far as we know had no formal training in forensic anthropology and had not examined large numbers of skeletons (if any at all), was ahead of his time in the forensic analysis of skeletal remains? It is unreasonable to view Hoodless, or any analyst of that time or this, as capable of making such assessments without error. Modern forensic anthropologists with training and experience still make errors, and the need to have estimates of error rates is receiving increased attention in view of the Daubert ruling.3 Cognitive bias (i.e., bias resulting from prior information) is especially problematic when making visual assessments (Nakhaeizadeh et al. 2014). We do not know whether cognitive bias may have played a role in Hoodless’s evaluation, but the possibility cannot be ruled out. We can agree that Hoodless may have done as well as most analysts of the time could have done, but this does not mean his analysis was correct. All we now have are the few measurements he gave in his report and his brief summary of the methods he used. It is important to extract as much as possible from the information at hand. In doing so, I will show that Cross and Wright (2015) present Hoodless as more unerring in forensic anthropology than most anthropologists of his time, and further that they have misinterpreted some of the other data available about Amelia Earhart. Stature Estimation Hoodless estimated stature using Pearson’s (1899) formulae. He cannot be faulted for this, because little else was available at the time. Cross and Wright (2015) argue that Pearson’s formulae are still in use today. I am not aware of any contemporary forensic anthropologist that uses Pearson’s formulae. Recent forensic anthropology textbooks either mention Pearson as important in developing the regression approach still in use today but omit his formulae, or do not mention him at all. Guharaj (2003) does include Pearson’s formulae, but, interestingly, includes the same erroneous constant for the radius that Hoodless used. This suggests that neither Guharaj nor Hoodless consulted Pearson’s original paper. Their shared error must go back to a common source. I have computed estimates from the more recent stature estimation criteria contained in Fordisc 3.1 and compared them to Pearson’s (Table 1). Pearson’s equations consistently underestimate height compared to modern criteria. Only one of Pearson’s estimates exceeds the 20 more-modern estimates in Table 1. Pearson’s male tibia estimate exceeds the 20th-century female forensic stature estimate. By any reasonable standard, the height of 65.5 inches (166.4 cm) presented by Hoodless and supported by Cross and Wright (2015) must be considered an underestimate. If the bones actually belong to a male, as Hoodless concluded, then the best estimate of height is about 170 cm, or about 67 inches. If the bones belong to a female, then about 169 cm, or 66.5 inches, is the most reasonable estimate. Using Pearson’s equation for females yields a height of circa 161–163 cm (63–64 in.), seemingly a serious underestimate. An examination of Pearson’s sample will clarify why his equations are not appropriate for modern people. Pearson used Manouvrier’s French sample, consisting of only 50 individuals of each sex. These were individuals whose birth years would likely have been early 19th century and who were substantially shorter than modern Americans or even Americans of the late 19th century. Pearson used an estimate of 165 cm to calculate the intercept for his male equations. This agrees well with Fogel’s (2004) values of 164.3 cm and 165.2 cm for French males reaching maturity in the first and second quarter of the 19th century, respectively. French women were estimated by different methods to arrive at a value of 152.3 cm. By contrast, American males born in the 1890s were 169.1 cm and in the first decade of the 1900s were 170.0 cm (Floud et al. 2011), some 4–5 cm greater than early-19th-century French. Floud et al. (2011) do not present data for females before 1910, but those born in that decade were 160.6, some 8 cm greater than the French value used by Pearson.
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Post by Admin on Mar 15, 2018 18:40:27 GMT
Figure 1 shows an example, using the humerus, of the relationship between bone length and stature. It illustrates the nature of the differences between Pearson’s sample and Trotter and Gleser’s (1952) 19th-century samples. The slopes are approximately equal, but the 19th-century regression lines are elevated, yielding higher estimates for a given bone length. Parenthetically, it is curious that Hoodless characterized the bones as possibly those of a “short, stocky muscular European,” when his own height estimate places the individual only slightly below the average for both American and European males born at the end of the 19th century and early in the 20th century. Hoodless’s Sex Assessement Cross and Wright (2015) argue that sex is the Earhart disqualifier, and indeed it could be, if firmly established. They are at some pains to present Hoodless as possessing sufficient expertise to leave little doubt about his sex assessment. Hoodless’s self-reported criteria were (1) half subpubic angle; (2) “set” of the femora; and (3) ratio of the long bone circumferences to their lengths. Cross and Wright (2015) go on to say these features are still used today. I am unaware that “set” of the femora and ratio of circumferences to length are used as a sexing criterion by forensic anthropologists practicing today. Evaluating these variables with data will demonstrate why they are not used. I will also show that estimating sex from the half subpubic angle is by no means foolproof. FIG. 1—Comparison of Pearson’s regression lines (short dashes = females, long dashes = males) with Trotter and Gleser’s 19th century (dotted = females, solid = males). The lengths of the lines on the x axis are set at ±2 standard deviations from their respective means. The shorter lines associated with Pearson’s data show lower variance compared to 19th-century Americans. The triangles are the position of the Nikumaroro humerus. Note that the Nikumaroro point for Pearson females is close to the upper maximum, where estimation is more unreliable, especially with small sample sizes. Ratio of femur circumference to length. Although Hoodless apparently used the ratio of circumference to length of several long bones, I will use the ratio of femur circumference to its length as an example of this approach. Femur circumference alone is dimorphic enough to qualify as a moderately good sex estimator (DiBennardo & Taylor 1979; Black 1978), but I have been unable to locate published references to use of the ratio of circumference to length as a dimorphic trait to estimate sex. No reference was provided by Cross and Wright (2015). Whether the ratios Hoodless employed are dimorphic enough to provide an indication of sex is subject to empirical verification. Table 2 shows discrimination statistics, using Euro-American femur data from the FDB for the circumference ratio, circumference alone, and femur length alone. Classification efficiency was assessed using an index of discrimination defined by Maynard-Smith et al. (1961) as (xm − xf)/(sdm + sdf), the difference between sex means divided by the sum of the standard deviations. The percentage of correct classifications can be estimated by relating the index to a cumulative normal distribution. This provides a close approximation to empirical classification rates. The best single variable is circumference, sexing around about 80% correctly. Femur length yields almost 78%. The sex difference in the ratio of circumference to length is highly significant, showing that males have a more robust midshaft than females. But the accuracy of assessing sex this way is 60%, only about 10% better than guessing. The ratio dilutes dimorphism, so it is almost 20% worse than circumference alone. “Set” of the femora. Using the femur for sex estimation is now common (Spradley & Jantz 2011), but I have been unable to find any reference to “set” of the femora, clarified by Cross and Wright (2015) as the angulation to the pelvis. Presumably it has something to do with angle of the femur neck and the distal condyles to the diaphysis. The angle of the distal condyles to the diaphysis was included in Dibenarrdo and Taylor’s (1983) analysis of sex and ancestry variation of the femur. For Euro-Americans of the Terry collection these values were 79.8 and 78.1 for males and females, respectively. The standard deviations were 2.1 for both sexes. The sex difference is small and significant (t = 4.5, df = 128, p < 0.001), but the overlap of the two distributions is too large to allow reliable sexing. Estimating accuracy from the index of discrimination yields an expectation of about 65% correct. It is slightly better than the ratio of circumference to length, but still only 15% better than guessing, not something that could be used to reliably assess sex. The sex difference of 1.7° would presumably be very difficult to appreciate via visual assessment. The angle of the femur neck to the diaphysis is no better. Anderson and Trinkaus (1998) could not identify consistent sex differences among world populations. In a sample of modern Euro-Americans the sex difference was 1.9°, which was not significant and would be difficult to appreciate by visual inspection. Half subpubic angle. The subpubic angle is defined as the angle formed by the two ischio-pubic ramii with an apex at the inferior junction of the pubic bones. This feature is undeniably a dimorphic feature, and in the hands of an experienced forensic anthropologist it can yield high accuracy rates, although not 100%. While it can be measured, in my experience that is rarely done by forensic anthropologists. The half subpubic angle requires assessing the angle from a single innominate, presumably more difficult than assessing it when both are present. There are some issues that reduce the certainty of Hoodless’s estimate. Especially important is Hoodless’s description of the condition of the bones: “All these bones are very weather-beaten and have been exposed to the open air for a considerable time. Except in one or two small areas all traces of muscular attachments and the various ridges and prominences have been obliterated.” (W.P.H.C.:15) Damage to the bones was most likely due to scavenging by crabs, as originally observed by Gerald Gallagher, administrator of the Phoenix Island settlement scheme, who also opined that the bones were from a female based on association with a women’s shoe sole.4 The fragile pubic bones would have been especially susceptible to damage. It is not beyond imagination that bone morphology was sufficiently modified to reduce ability to accurately assess the half subpubic angle. Even without taphonomic change, sex estimates can vary widely. A method put forth by Phenice (1969) is commonly accepted as reliable. The Phenice method uses three features of the pubic bone, including the subpubic contour. It should be noted that the subpubic contour does not entirely define the subpubic angle, but as Klales et al. (2012) note, the female concavity results in a greater subpubic angle, which would likely play a large role in visual assessment of the subpubic angle. Klales et al. (2012) present the results of eight tests of the Phenice method. They range from 59% to 99% in sexing accuracy. Of the eight tests presented, four sexed correctly at less than 90%. These tests used all three of Phenice’s traits; presumably the subpubic contour alone would perform worse than all three combined. FIG. 2—Barchart of ordinal scores for the subpubic contour, which forms one half of the subpubic angle. A substantial minority (20%) of females (white bars) have scores that are either ambiguous (SC = 3) or male (SC = 4 or 5). Data from Klales et al. (2012). Klales et al. (2012) have devised a systematic, five-stage ordinal scoring system for the Phenice traits, including the subpubic contour. Part of their sample was drawn from the Hamann-Todd anatomical collection, which is a reasonable reference sample for the Nikumaroro bones. Figure 2 shows the distribution of the Hamann-Todd sample on the five-stage scores of Klales et al. (2012). The scores range from strongly female (stage 1) to strongly male (stage 5). The graph shows that most females are stage 1 or 2, and most males are stage 4 or 5. But there is a sizable minority of females (21% of the female sample) in stage 3 or higher. Stage 3 is the antimode between the two distributions and describes an ambiguous subpubic contour that could easily be called either male or female. Klales (2016) has documented that the subpubic contour has experienced secular change, the number of ambiguous females declining since 1940. These data suggest that Hoodless could easily have been presented with morphology that he considered male, even though it may have been female.
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Post by Admin on Mar 17, 2018 18:52:19 GMT
Overall Assessment of Hoodless’s Sex Estimate Hoodless based his conclusion on three features, one of which—the ratio of circumference to length, as exemplified by the femur—is not sufficiently dimorphic to provide useful information. The second feature, “set” of the femora, is also minimally informative. The subpubic angle, the most reliable of Hoodless’s criteria, is also subject to considerable variation, much of which was little understood in 1941. We do not know what weight Hoodless attached to each feature. He must have considered the two doubtful features to some degree, and perhaps given them weights equal to the subpubic angle. Otherwise he would not have mentioned them. Cross and Wright (2015) argue that Hoodless undoubtedly made an overall assessment of the remains, including the skull, but only reported the less detailed information appropriate to his audience. How this overall assessment might have informed his decision is pure speculation. No one knows what the skull or postcranial skeleton looked like, nor what Hoodless used to arrive at his assessment of robusticity. It is also worth noting that while demonstrating awareness of Pearson’s (1899) stature estimation paper, Hoodless was either unaware of or chose not to mention Pearson and Bell’s (1919) paper—which provided valid sexing criteria for the femur, such as the femur head diameter. The state of the art at the time, and the fact that Hoodless was not an experienced forensic anthropologist, reduce the reliability of Hoodless’s sex estimate considerably below that accorded it by Cross and Wright (2015). The most prudent position concerning sex of the Nikumaroro bones is to consider them unknown. Hoodless’s Ancestry Estimate It is the case, as Cross and Wright (2015) have stated, that little convincing evidence concerning the ancestry of the Nikumaroro bones can be gained from the four cranial measurements Hoodless provided. However, this is not to say we cannot get more evidence than offered by Hoodless, or by Cross and Wright (2015). Hoodless’s assessment that the skeleton is not full Pacific Islander but could be a “short stocky, muscular European or even a half-caste or a person of mixed European descent” (W.P.H.C.:15) may reflect assumptions that conflict with his own assessment of the two indices he computed—orbital and cranial—both of which indicated European. Cross and Wright’s (2015) CRANID analysis is flawed because they included samples from all over the world, most of them including individuals from populations that had zero or near zero probability of having been on Nikumaroro. Konigsberg et al. (2009) have shown the importance of an informative prior probability in ancestry estimation. If the prior probability is zero, then the posterior probability must also be zero. If the problem is approached using only samples of populations that might reasonably have been on the island, somewhat more definitive results are obtained. Ancestries other than European would include Micronesians and Polynesians. I use a Euro-American sample of the early 20th century, a Micronesian sample (Guam), and a Polynesian sample (Moriori), the last two from Howells’s data. Ideally the Micronesian sample should come from the Eastern Micronesians, but data are limited. Pietrusewsky’s (1990) samples are small and limited to males, but they argue for a basic continuity among Micronesians. The same is true for Polynesians, so Guam and Moriori can be accepted as reasonable representations of these two areas. Table 3 shows Fordisc results for Euro-Americans and Pacific Islanders, each with both sexes. The lowest Mahalanobis distance and the highest posterior probability belong to early-20th-century Euro-American females. Because the discriminating ability of four measurements is low, the skull cannot be excluded from any of the populations used, as shown by the typicality probabilities. The Typ R, the ranked typicality probability column, provides some additional useful information. Typ R is the ranking of each skull’s distance from the sample mean. A typicality probability of 1.0 would indicate that all the values are identical to the mean. Euro-American females have the highest typicality probability. Only 6 crania of 90 are more typical than the Nikumaroro skull. Typicalities for all other groups are 0.65 or less. Another avenue toward ancestry assessment could lie in the long bone lengths, since different populations have different long bone proportions. This can be approached quantitatively using distance statistics parallel to those used for the cranial analysis. We do not have a database containing bone lengths from different populations, but it is possible to use published means as long as one has a covariance matrix. It has been shown that the long bone length covariance matrices from widely different populations are homogeneous (Holliday & Ruff 2001). Therefore I use mean long bone lengths from Hawaiian and Chomorro people as representative of Pacific Islanders (Polynesia and Micronesia) (Ishida 1993), and 19th-century (Terry collection) and 20th-century Whites (FDB) from which the covariance matrix was obtained.
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Post by Admin on Mar 19, 2018 18:46:54 GMT
Figure 3 shows the distances plotted on the first two canonical axes obtained from humerus, tibia, and radius length. The first axis is mainly size and therefore reflects sex differences. The second axis reflects mainly humerus and tibia lengths, low scores reflecting longer humeri and tibiae. The Nikumaroro bones were interpolated into the plot using the distances from each group as described by Gower (1972). The Nikumaroro bones are most similar to White males. They are most distant from Pacific Islanders, particularly Chomorro Micronesians. FIG. 3—Canonical plot of Euro-Americans, Hawaiians, and Chomorro from bone lengths. The Nikumaroro bones were interpolated into the plot using distances from other groups. The first axis mainly reflects size and hence sex differences. The second axis mainly reflects humerus and tibia lengths, low scores reflecting longer humeri and tibiae. The Nikumaroro bones fall on the male side on CV1 and on the Euro-American side on CV2. Amelia Earhart’s Height, Weight, Body Build, and Limb Lengths and Proportions I will now try to reconstruct what I can about Amelia Earhart’s, height, weight, body build, and limb lengths and proportions. This will serve two purposes: (1) allow testing of Cross and Wright’s (2015) assumption that she was extremely linear and gracile, and (2) allow explicit evaluation of the Nikumaroro bones against Amelia Earhart to determine whether she can be excluded or included. Height The source routinely employed for Amelia Earhart’s height has been her pilot’s license, where 5'8" is recorded. This is called a forensic stature, meaning that it comes from a document rather than being explicitly measured. The air commerce regulations for 1928 state the following: An application for a pilot’s license must be filed, under oath, with the Secretary of Commerce upon blanks furnished for that purpose. An applicant for a pilot’s license, including a student’s pilot license, must appear for a physical examination before a physician designated by the Secretary of Commerce and pass such examination, unless he is exempt under these regulations. There appears to be no explicit requirement that height must be measured. If it was measured, it could have been done either freestanding or standing against a wall. We have no idea of the skill or attention to detail the examiner might have brought to the task. Was Earhart properly positioned with shoes off? Was the instrument properly calibrated? Did the examiner round; for example, did 67.5 inches become 68 inches? All of these can introduce variation into the measurement. Or the examiner may merely have asked Earhart how tall she was. FIG. 4—Amelia Earhart’s 1927 Massachusetts driver’s license showing her height as 5'7", one inch shorter than that given on her pilot’s license. Driver’s licenses are commonly used as sources of forensic statures. Figure 4 shows Earhart’s Massachusetts driver’s license for 1927, where 5'7" is recorded. It is unlikely that the height on her driver’s license was measured. It is a forensic stature that is as valid as the one on her pilot’s license. This makes the point that height is not a fixed attribute that is measured or reported consistently. It was therefore necessary to seek a measured height which can be obtained photographically by scaling her to known dimensions of an aircraft. Glickman (2016a) estimates her height at 67.125 inches, almost an inch less than the height reported on her pilot’s license but in agreement with her driver’s license. Glickman’s height has the advantage that it was measured, the methods described, and it is subject to verification. While the difference between the forensic heights and measured height is relatively inconsequential, I will use the measured height of 67 inches for the remainder of the paper. Whether she was 5'8" or 5'7", Earhart was a tall woman for the time in which she lived. This can be illustrated by comparing her height to anthropometric data collected on Pembroke College Women in 1927 by A. M. Tousley and on University of Tennessee women measured in 1930 by I. G. Carter, both series reported by Carter (1932). If Amelia Earhart was 67 inches (170 cm) tall, she was taller than 85% of Pembroke College women and 92% of University of Tennessee women. If she was 68 inches (172.7 cm) tall, she was taller than 88% of Pembroke College women and 97% of University of Tennessee women. Males of her birth cohort were 169.1 cm (Floud et al. 2011), so Earhart was slightly taller than the average male of her time. It turns out, too, that American “high society” women of the 19th century were substantially taller than average and seemed to be immune to the stature decline affecting the general population (Sunder 2011). Sunder estimates the average height of high society women, which probably includes Earhart, at the end of the 19th century at 64.9 inches (164.8 cm), more or less equal to what it is today.
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