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The Adult Human Occipital Bone: Measurement Variance and Observer Error
Abstract
The adult human occipital bone offers opportunities to develop measurements that can aid in the identification of human remains, particularly as it tends to survive inhumation and physical insults more readily than many other bones of the skull. The occiput has a number of anatomical features, some of which have been evaluated for sex and ancestry differences including the occipital condyles and the foramen magnum. Using these features, ten measurements of the occipital region were chosen from past publications. In addition, the position of the hypoglossal canals offered an opportunity to develop two new measurements. Twenty skulls of unknown sex and ethnicity were obtained, their occipital regions examined, and a number of measurements performed. Twelve measurements were recorded to two decimal places using digital (Mitutoyo) sliding calipers. Parts A, B and C of this experiment examined intraobserver error, multiobserver error and variation between twenty skulls by using the coefficient of variation. This study aimed to define and evaluate measurements that may be used in identification of human cranial remains, and forms part of a wider study on sexual differences of the condylar region of the human occipital bone. These initial results indicate that while all measurements have the potential to prove useful, the bicondylar breadth, the distance between the external hypoglossal canals, the length of the foramen magnum and the width of the foramen magnum are the most clearly defined, and may offer greater potential in sex identification.
... The traditional methods of recording measurements of the cranial base include the use of spreading calipers and calibrated paper strips [26]. Some of the problems associated with these methods have been outlined in past publications [5,36]. ...
... For the St. Bride's crania, manual measurements were chosen from past publications [5,14,26,36]. ...
... All measurements were recorded to two decimal places. Intraobserver and interobserver errors for these measurements were analysed by two of the authors in a previous publication [5]. The St. Bride's measurements were recorded by a single observer (RG) using the same equipment. ...
The successful identification of the deceased is vital to the progress of any forensic investigation. One of the principal biological traits to be established from skeletal remains is the sex of the individual. This becomes more difficult if only parts of a skeleton are found or if the bones are compromised by physical insults such as fire, explosions or violence. The basal region of the occipital bone is covered by a large volume of soft tissue and is therefore in a relatively well-protected anatomical position, and as such, classification of sex using the occipital bone may prove useful in cases of significantly disrupted remains. The aim of this paper is to evaluate manually recorded morphometric variables of the region of the foramen magnum using both discriminant function analysis and linear regression. The skulls utilised in this study were selected from the eighteenth to nineteenth century documented skeletal collection of St. Bride'fs Church, Fleet Street, London. Adult human skulls n = 158 (permil;82/76) were measured to derive statistical functions. The results demonstrated that significant sexual dimorphism is present in the cranial base of the St. Bridefs material. The correctly classified crania within this population ranged from 65.8% for univariate functions to 70.3% for multivariate functions within the cranial sample. Males were correctly classified at 70.7% and females at 69.7% using multivariate functions. The linear regression equations predicted sex in the cranial sample correctly for 76% of the males and 70% for the females using different variables; however, overall highest correct prediction percentage was only 68%. Cross-validation brought the percentage down in some cases, but it was concluded that, overall, the expression of sexual dimorphism in the foramen magnum region within the St. Bridefs population is significantly demonstrable, and therefore, this area of the skull should be considered useful in the identification of sex.
... The determination of gender for unidentified human remains is a key aspect for forensic anthropologists as this information can be used for legal investigations or the study of past populations [2] [8] [9]. In this regard, forensic anthropologists work in conjunction with homicide investigators in order to identify unique features (sex, age, ancestry, stature, etc.) of the deceased person from skeletal remains. ...
... The performance of the devised machine vision solution was evaluated by cross correlating the results obtained by the semi-automatic technique and the manual measurements obtained by the Forensic Anthropology Unit in University College Dublin (UCD) [2]. For this purpose, we have selected 5 skulls (labelled as skull 6, 9, 11, 13 and 14) and the results for LFM, WFM and FMA obtained by the developed system are compared with those obtained by manual measurements. ...
... The determination of gender for unidentified human remains is a key aspect for forensic anthropologists as this information can be used for legal investigations or the study of past populations [2,8,9]. In this regard, forensic anthropologists work in conjunction with homicide investigators in order to identify unique features (sex, age, ancestry, stature, etc.) of the deceased person from skeletal remains. ...
Human skeletal remains are analysed by forensic anthropologists in order to draw conclusions about the
probable identity of the deceased. During the analysis, the skull is used, along with other bones, to help
determine the identity of the decedent. If only the base of the skull is available, forensic researchers take
manual measurements from the large oval aperture in this region, the foramen magnum, in order to obtain
information about the gender of the deceased. As this operation requires human intervention, the
measurements are affected by the bias introduced by the human operator. The aim of this paper is to describe
a full machine vision solution to perform precise morphological measurements of the foramen magnum. The
system has been designed to extract measurements from 2D and 3D data and the returned results accurately
match the manual measurements.
... The absolute technical error of measurement (TEM), relative technical error of measurement (rTEM), and coefficient of reliability (R) were calculated following Perini et al. (2005) and Gapert et al. (2009b) to assess the degree of magnitude of the random error of measurement. Inter-observer error rates for the measurements used can be found in Gapert and Last (2005) and Wescott and Moore-Jansen (2001). ...
... As this paper used published data, it was not possible to undertake interobserver error tests, and it is possible that this may play a role in the differences between the samples. Research has shown that with the exception of the occipital condyle width and length, the dimensions of the basal occipital assessed here can be well replicated (Gapert and Last 2005;Wescott and Moore-Jansen 2001) which suggests that inter-observer error can be limited with careful measurement. Here, every care was taken to minimize this error which is reflected in the intra-observer tests results. ...
Multiple discriminant functions that estimate sex from the dimensions of the basal occipital have been published. However, as there is limited exploration of basal dimension variation between groups, the accuracy of these functions when applied to archaeological material is unknown. This study compares basal dimensions between four known sex-at-death post-medieval European samples and explores how metric differences impact on the accuracy of sex assessment discriminant functions. Published data from St Bride’s, London (n = 146) and the Georges Olivier collection, Paris (n = 68) were compared with new data from the eighteenth to nineteenth century Dutch Middenbeemster sample (n = 74) and the early twentieth century Rainer sample, Romania (n = 282) using independent t tests. The Middenbeemster and Rainer data were substituted into six published discriminant functions derived from the St Bride’s and the Georges Olivier samples, and the results were compared to their known sex. Multiple statistically significant differences were found between the four groups. Of the six discriminant functions tested, five failed to reach the published accuracy and fell below chance. In addition, even where the samples were statistically comparable in means, trends for difference also impacted the accuracy of discriminant functions. Enough variation in basal occipital dimensions existed in the European groups to decrease the accuracy of sex estimation discriminant functions to unusable. Possible inter-observer error, varying genetic, socioeconomic, and geographical factors are likely causes of dimension variation. This research further highlights the dangers of using sex estimation discriminant functions on samples that differ to the original derivative population and demonstrates the need for more rigorous testing.
... OCW is relatively easy to measure and can be unambiguously recognized by different observers. Previous studies have found that OCW is an extremely replicable measurement, at least among features of the occiput, and shows low inter-observer bias [163]. Furthermore, because OCW is a cranial measurement, it does not require associated postcrania to estimate mass (as is the case for limb bones) or a relatively complete specimen with undistorted skull and spinal column (as is the case for HBL). ...
Background
Body mass estimation is of paramount importance for paleobiological studies, as body size influences numerous other biological parameters. In mammals, body mass has been traditionally estimated using regression equations based on measurements of the dentition or limb bones, but for many species teeth are unreliable estimators of body mass and postcranial elements are unknown. This issue is exemplified in several groups of extinct mammals that have disproportionately large heads relative to their body size and for which postcranial remains are rare. In these taxa, previous authors have noted that the occiput is unusually small relative to the skull, suggesting that occiput dimensions may be a more accurate predictor of body mass.
Results
The relationship between occipital condyle width (OCW) and body mass was tested using a large dataset (2127 specimens and 404 species) of mammals with associated in vivo body mass. OCW was found to be a strong predictor of body mass across therian mammals, with regression models of Mammalia as a whole producing error values (~ 31.1% error) comparable to within-order regression equations of other skeletal variables in previous studies. Some clades (e.g., monotremes, lagomorphs) exhibited specialized occiput morphology but followed the same allometric relationship as the majority of mammals. Compared to two traditional metrics of body mass estimation, skull length, and head-body length, OCW outperformed both in terms of model accuracy.
Conclusions
OCW-based regression models provide an alternative method of estimating body mass to traditional craniodental and postcranial metrics and are highly accurate despite the broad taxonomic scope of the dataset. Because OCW accurately predicts body mass in most therian mammals, it can be used to estimate body mass in taxa with no close living analogues without concerns of insufficient phylogenetic bracketing or extrapolating beyond the bounds of the data. This, in turn, provides a robust method for estimating body mass in groups for which body mass estimation has previously been problematic (e.g., “creodonts” and other extinct Paleogene mammals).
Paper currently available as open access at https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-021-01224-9.
... Interobserver error analysis of the foramen magnum and occipital condyle measurements has been previously published by Gapert and Last [72]. ...
Sex differences in the foramen magnum region of the cranial base have been identified with varying rates of success. Recent publications demonstrate a continuing strong interest in metric analysis of the foramen magnum region for sex determination despite the generally low expression of cranial base sexual dimorphism. It is important to identify possible age effects on skull base morphometric variables as most reported discriminant analyses use pooled-age samples without assessing the influence of aging on sexual dimorphism. This study examined 135 adult cranial bases (69 males and 66 females) from the St. Bride's documented skeletal collection in London. Traditional craniometric measurements were recorded and the effect of age on sexual dimorphism of this anatomical region was tested using a variety of statistical analyses including MANOVA and discriminant function analysis. Age-dependent discriminant functions for <50 and >50 years of age were developed and compared. The cross-validated results showed that the <50 years function determined the sex of 69.1 % correctly while the >50 years function achieved 81.3 % correct predictions. However, the high sex biases of these functions (14.4 % and -17.5 %) severely limit their practical application. A pooled-age discriminant function permitted 71.9 % correct prediction with a sex bias of only -1.7 %. The statistical analyses also showed no significant age effect on any of the variables, suggesting that a separation by age is not necessary for the development of sex determination methods.
... The values observed for the relative technical error of measurement (rTEM) reveal that LFM and breadth (WFM) dimensions of the foramen magnum are the most reliable (0.2784 and 0.4551%, respectively), while MxID is the variable most difficult to replicate (3.9 979%). These results are consistent with previous studies concerning the basal region of the occipital bone [1,7,21]; although Wescott et al. found width of the occipital condyle (MWC) to be the most unreliable measurement [7]. ...
The determination of sex from human skeletal remains is of fundamental importance in both medicolegal and bioarchaeological investigations. In the present study, the basal region of the occipital bone in a documented French collection was analyzed for sex differences using standard osteometric techniques. The results demonstrated that a low level of sexual dimorphism is present in the cranial base of this sample, with few of the measured variables exhibiting statistically significant differences between the sexes. The cross-validated classification accuracies obtained in this study for the derived discriminant functions are appreciably lower than those previously reported for other disparate populations. A stepwise procedure, which selected maximum length of the left occipital condyle and minimum distance between occipital condyles (MnD), produced the best overall result with a classification accuracy rate of only 67. 7%. The most effective single dimension, bicondylar breadth (BCB), also correctly classified 67. 6% of the individuals examined, but with a much higher sex bias. Osteometric analysis of cranial base dimensions, therefore, cannot be regarded as a sufficiently reliable method for determining sex in this population group. © 2010 Société d'anthropologie de Paris et Springer-Verlag France.
... Both stepwise and direct discriminant analysis were used to calculate specific discriminant formulae that can be applied to fragmentary remains. Observation errors in measuring any parameter and error of measurements may occur because of ill-defined landmarks (42). A paired t-test was performed so, to determine intra-observer error for all variables including the four newly developed measurements (parameters 1,2,4,6). ...
Determination of sex from fragmentary crania is a critical problem in forensic anthropology. Osteometric analysis of mastoid can serve forensic anthropologists better in sex identification by virtue of the noticeable dimorphic characteristics. The present study aims to develop population-specific, sex-differentiating anthropometric standards for the mastoid process of North Indian skulls. Eight parameters of the mastoid region were measured on 138 adult crania (M/F 104:34, 22-65 years) and analyzed using SPSS 16.0. All parameters showed significant sexual dimorphism (p < 0.000). In stepwise analysis, asterion-mastoidale and mastoid breadth have provided an accuracy of 87%. Receiver operating characteristic curves were obtained for each variable to observe their overall performance in sex determination. Posterior end of incisura mastoidea-depression of suprameatal triangle was found to be the best variable with maximum area under curve and highest predictive accuracy (82.6%).
... The protected position of the atlanto-occipital region may aid in the survival of the condyles when the rest of the cranium has disintegrated. Traditional methods of recording measurements of the cranial base have been outlined before (Martin and Saller, 1957;Droessler, 1981;Routal et al., 1984;Holland, 1986;Westcott and Moore-Jansen, 2001;Gapert and Last, 2005). Sex differences in the foramen magnum region of the cranial base have been examined with varying success rates (Teixeira, 1982;Routal et al., 1984;Holland, 1986;Gü nay and Altinkök, 2000;Westcott and Moore-Jansen, 2001;Murshed et al., 2003;Gapert et al., 2008). ...
Fragmentary human remains compromised by different types of inhumation, or physical insults such as explosions, fires, and mutilations may frustrate the use of traditional morphognostic sex determination methods. The basicranium is protected by a large soft tissue mass comprising muscle, tendon, and ligaments. As such, the occipital region may prove useful for sex identification in cases of significantly fragmented remains. The aims of this paper are to (1) evaluate sexual dimorphism in British cranial bases by manually recorded unilateral and bilateral condylar length and width as well as intercondylar measurements and (2) develop discriminant functions for sex determination for this cranial sample. The crania selected for this study are part of the 18th-19th century documented skeletal collection of St. Bride's Church, Fleet Street, London. Adult human skulls (n = 146; male75/female71) were measured to derive statistical functions. Results indicated that expression of sexual dimorphism in the occipital condylar region within the St. Bride's population is demonstrable but low. Crossvalidated classification accuracy ranged between 69.2 and 76.7%, and sex bias ranged from 0.3 to 9.7%. Therefore, the use of discriminant functions derived from occipital condyles, especially in British skeletal populations, should only be considered in cases of fragmented cranial bases when no other morphognostic or morphometric method can be utilized for sex determination.
Correct scoring of caries lesions is a fundamental step in the bioarchaeological investigation of past populations. The present and the extension of caries lesions inform us about past subsistence and diet, human behaviour, social inequality and overall health status through time. We asked ourselves how relevant an interpretation of a past society’s dependence on dental caries identification might be with an interest in demonstrating the quality of the primary data and the need for precise evaluation. We tested an assessment agreement of dental caries among observers from different subject fields. Two dentists and two anthropologists visually investigated 233 teeth and 3029 teeth surfaces from archaeological samples at the Plzeň “U Zvonu” cemetery dating to medieval and early modern times. We made use of Cohen kappa and Fleiss’ kappa to calculate the inter-observer and intra-observer agreement. The results indicate that the overall prevalence of dental caries in the tested assemblage ranged from 1% to 6%, depending on the observer. The inter-observer agreement decreased from an average of k=0.77 (identification of teeth) to k=0.40 (evaluation of the extent of caries lesion). Assessment in the caries extension decreased more rapidly having been caused by the in all probability increasing demands of individual observation. We recorded homogeneity in the assessment of each observer in the intra-observer agreement with the exception of Dentist 2. We did not record a dependence on the subject field of the observer. The most probable cause of low inter and high intra-observer agreement could be in the methodological process of each observer, precision in the application of the methodology and the responsibility of the individual observer.
Sex and race variation of the occipital bone have been previously investigated, but particular examination of the effect of age and ancestry on sexual dimorphism has not been addressed. This paper examines morphological variation associated with sex and ancestry in the condylar region of the occipital bone and the effect of age and ancestry on the estimation of sex. Models previously published by Holland are also tested, and methodological problems are addressed. The results indicate that age does not have an effect on sexual dimorphism, but that whites exhibit greater, although not significantly, more sexual dimorphism than blacks. Significant sex and ancestry variation is present in the condylar region of the occipital bone, but neither sex nor ancestry could be estimated accurately using measurements of this anatomical region defined by Holland.
Sex determination in unidentified skeletons is not always easily and correctly performed by a non-specialist without formal training in forensic anthropology. In explosions, warfare and other mass disasters like aircraft crashes, identification may be extremely complicated because of skeletal fragmentation. The aim of the present study was to determine whether the area of the foramen magnum was a useful criterion for the sex determination in fragmented skulls. In a total of 219 skeletons (170 males and 39 females) the longest and the shortest diameter of the foramen magnum was measured; the area within was determined using the mean of the diameters as the radius for calculation. The mean of foramen magnum area was significantly different (909.91 +/- 126.02 mm2 in males, 819.01 +/- 117.24 mm2 in females homogeneous variance, Student's t-test: 4.11 P< 0.001). However, the correlation coefficient between the areas of foramen magnum and sex was 0.27. The results confirmed that the mean foramen magnum area in females is lower than in males. However, the area of foramen magnum is not a very useful indicator for sex identification and can be used only under some circumstances as a supportive finding.
A biometric study of the occipital bone was carried out on 125 dissecting room skulls; it brought out the following points: 1. The occipital squama, despite its dual histological origin, constitutes a stable anatomical structure because its dimensions remain in correlation if the size factor is maintained constant. 2. The parts around the foramen magnum also show 'organic correlations', but these are virtually unrelated to the squama. 3. The pars basilaris is biometrically independent of the squama; it could well be described with, and regarded as an extension of, the body of the sphenoid if it were morphologically separated from the rest of the occipital bone; there is thus good cause to describe in Man a spheno-occipital 'clivus'. 4. The study of the curvatures of the squama shows that fossil Man agrees with present day Man in that when the occipital is rounded, the parietal is not, and the skull is low and elongated. 5. Sexual differences are more easily described than measured. The shape of the occipital condyles has greater value for sex determination than that of the nuchal crests. 6. Attempts were made to estimate cranial capacity from isolated occipital bones, but one had to be content with a fairly large margin of error. Several types of formulae are nevertheless offered to human palaeontologists in the hope that they might satisfy their need to get a rough indication of cranial capacity from occipital material.
The cranial base can be used to determine the sex of fragmentary or deformed skulls. An initial study used nine measurements taken from 100 crania in the Terry Collection. The sample was divided equally by race and sex. Six regression models were formulated that predicted correctly the sex of the sample with 71-90% accuracy. In a separate test, a control sample of 20 skulls, also drawn from the Terry Collection but not involved with formulating the regression equations, was correctly classified with 70-85% accuracy.
The sex of unidentified skeletons is not always easily and correctly determined by the general medical examiner with no formal training in forensic anthropology. Sometimes the diagnostic procedure may be extremely complicated when handling fragmented bones. The present preliminary observations concern the evaluation of the size of the foramen magnum in 40 skulls (20 of each sex). Our results indicate that this method may be useful in the sexing of skeletal remains under the above-mentioned conditions as well as when an expert in forensic anthropology or a crime laboratory is not available.
ASURVEY OF THE medical literature indicates that there has been no attempt to compare definitively skull radiographs of the male and female adult. Keen (1) has presented this problem from the standpoint of the anthropologist and it was felt that a comprehensive evaluation of the roentgenology would be of value and interest. It was also felt that such a study might be of some importance medicolegally. We have been encouraged by a personal communication (2) to develop this comparison. Methods The basis for this paper was the evaluation of 100 normal adult male and 100 normal adult female skull films. The ages of the male patients ranged from twenty to seventy-two years and the females from twenty-two to eighty-six years. The films were compared with regard to the following characteristics noted on the frontal projection (posteroanterior): 1. Sagittal diameter: Measurement of the distance from the top of the skull in the midline to the lower edge of the mandible in the same plane. 2. Mastoid length: Measur...
Sex determination offragmentary crania by analysis of the cranial base: applications for the study of an Arikara skeletal sample. Thesis
- Mm Williams
Williams MM (1987) Sex determination offragmentary
crania by analysis of the cranial base: applications for
the study of an Arikara skeletal sample. Thesis.
University of Tennessee.