Sex determination from an unknown human skeleton to identify an individual is an important aspect of forensic anthropology. Although DNA analysis is the most reliable method to identify an individual, it requires special tools and time. One simple method to identify sex is by using the skeletal remains. The identification of sex from skeletal remains is 100% reliable [1] if the entire skeleton is present; however, skeletal remains are often incomplete or fragmented. To identify sex, several studies used various bones, such as the mandible [2, 3, 4], scapula [5], pelvis [6, 7, 8, 9], and skull [4, 10, 11, 12, 13, 13, 14,15]. The pelvis is the most accurate bone for sex determination and can predict sex with an accuracy of >95% [1]. However, a complete pelvis is not always easily available. It is often necessary to use other bones for sex determination.
There are two major methods to determine sex from skeletal remains. The visual method is based on observation of morphological characteristics of sex, is easy to assess, and does not require measuring tools, but it is highly subjective and depends on the skill of the anthropologist [16, 17]. The osteometric measurement is a method of measuring the skeleton, requiring a specific tool for measurement, but is reliable, decreases the problem of the investigator’s subjective evaluation [17], and can be reevaluated easily in the assessment of sex. While the conventional technique of using calipers to measure bones has been used for years, the use of computer-aided design software for engineering and architecture, such as AutoCAD, has been reported to be successful in measuring the sacral base [17], acetabular rim [18], and frontal bone [19] for sex determination in the field of forensic anthropology.
Because it has been recognized that sexual characteristics are specific to each population due to genetics, environment, and culture, specific standards in one population cannot be applied to another group [1, 10]. Therefore, the purpose of this study was to determine sex from crania of Northern Thai using craniometry by digital photograph processing with AutoCAD and digital calipers.
The sample consisted of 160 dry skulls (84 men and 76 women) from the collection housed at the Department of Anatomy, Faculty of Medicine, Chiang Mai University, Thailand. The mean age at death of donors of this sample was 66.02 ± 12.61 years with no significant difference between the sexes (
Each skull was set on a sand bag with a black background and the same plane of reference for photography. A Canon EOS 1000D digital camera (10.0 megapixel) was used in this study. The digital camera was set on a stand with a fixed distance (300 mm) to take the photograph of the anterior and lateral views of the left side of the skull (
The landmarks of Krogman and Iscan [1] and Buikstra and Ubelaker [20] were followed (
Definitions of measurements
Abbreviation | Definition | Measurement |
---|---|---|
OrH† | Orbital height | Distance between orbitale to supraorbital margin |
D-Ec† | Orbital breadth | Distance between dacryon to ectoconchion |
NL§ | Nasal bone length | Distance between nasion and rhinion |
ENOH§ | External nasal opening height | Distance between rhinion and nasospinale |
APMH§ | Alveolar process of maxilla height | Distance between nasospinale and prosthion |
Zy–Zy† | Bizygomatic breadth | Distance between the right and left parts, or the widest part of the zygoma |
OrA§ | Orbital area | Area of orbital margin |
OrP§ | Orbital perimeter | Perimeter of orbital margin |
ENOA§ | External nasal opening area | Area of external nasal opening |
ENOP§ | External nasal opening perimeter | Perimeter of external nasal opening |
MTA‡ | Mastoid triangle area | Area of triangle drawn from three points (porion, mastoidale, and asterion) |
ZaA§ | Zygomatic arch area | Area of space between the line drawn from the frontomalare temporale to the zygomatic arch above the porion |
ZaP§ | Zygomatic arch perimeter | Perimeter of space between the line drawn from the frontomalare temporale to the zygomatic arch above the porion |
GBA§ | Glabella-bregma area | Area of space between the straight line drawn through bregma in the horizontal plane and perpendicular to the straight line drawn through the glabella in the vertical plane |
GBP§ | Glabella-bregma perimeter | Perimeter of space between the straight line drawn through the bregma in the horizontal plane and perpendicular to the straight line drawn through the glabella in the vertical plane |
†Parameters described by Krogman and Iscan [1] and Buikstra and Ubelaker [20]; ‡parameters described by Paiva and Segre [21]; §parameters created for the present study.
To evaluate the values of the measurements obtained from the AutoCAD technique, the length of OrH, D-Ec, NL, ENOH, APMH, and Zy–Zy were measured to compare with the values obtained from the digital calipers. An independent
To assess the intraobserver error, 30 crania were measured a second time after 1 month by the same observer, and a paired
The data were analyzed using SPSS Statistics for Windows software package (version 17.0, SPSS). Descriptive statistics, including the mean and standard deviation, were calculated. An independent
The mean and standard deviation for measurement of the cranium were calculated for both men and women, and the
Descriptive statistics of the cranium’s parameters using the AutoCAD method (
Parameter | Sex | n | Mean | SD | |
---|---|---|---|---|---|
OrH† | Male | 84 | 34.40 | 1.78 | <0.001 |
Female | 76 | 32.10 | 1.35 | ||
D-Ec† | Male | 84 | 38.64 | 2.51 | <0.001 |
Female | 76 | 35.42 | 1.55 | ||
NL† | Male | 84 | 24.38 | 2.84 | |
Female | 76 | 21.34 | 1.49 | <0.001 | |
ENOH† | Male | 84 | 28.40 | 2.75 | |
Female | 76 | 22.72 | 1.96 | <0.001 | |
APMH† | Male | 84 | 16.81 | 3.29 | |
Female | 76 | 17.62 | 2.33 | 0.08 | |
Zy–Zy† | Male | 84 | 126.23 | 6.52 | |
Female | 76 | 121.90 | 5.33 | <0.001 | |
OrA‡ | Male | 84 | 1032.80 | 93.06 | |
Female | 76 | 924.11 | 81.58 | <0.001 | |
OrP† | Male | 84 | 117.30 | 6.01 | |
Female | 76 | 115.43 | 5.14 | 0.04 | |
ENOA‡ | Male | 84 | 583.57 | 79.73 | |
Female | 76 | 548.95 | 41.61 | 0.001 | |
ENOP† | Male | 84 | 90.42 | 6.70 | |
Female | 76 | 88.34 | 5.31 | 0.03 | |
MTA‡ | Male | 84 | 686.33 | 91.769 | <0.001 |
Female | 76 | 591.07 | 76.43 | ||
ZaA‡ | Male | 84 | 724.95 | 108.41 | 0.002 |
Female | 76 | 679.75 | 62.39 | ||
ZaP† | Male | 84 | 149.07 | 10.79 | 0.014 |
Female | 76 | 145.07 | 9.48 | ||
GBA‡ | Male | 84 | 1010.86 | 138.17 | |
Female | 76 | 816.78 | 119.04 | <0.001 | |
GBP† | Male | 84 | 213.19 | 17.22 | |
Female | 76 | 183.87 | 17.92 | <0.001 |
†Measured in millimeters (mm); ‡Measured in square millimeters (mm2).
Descriptive statistics of the cranium’s parameters using the digital caliper method
Parameter | Sex | n | Mean | SD | |
---|---|---|---|---|---|
OrH† | Male | 84 | 34.40 | 1.79 | |
Female | 76 | 32.14 | 1.40 | <0.001 | |
D-Ec† | Male | 84 | 38.80 | 2.57 | |
Female | 76 | 35.42 | 1.58 | <0.001 | |
NL | Male | 84 | 24.36 | 2.86 | |
Female | 76 | 21.35 | 1.51 | <0.001 | |
ENOH† | Male | 84 | 28.41 | 2.76 | <0.001 |
Female | 76 | 22.74 | 1.96 | ||
APMH† | Male | 84 | 16.81 | 3.29 | <0.07 |
Female | 76 | 16.81 | 3.29 | ||
Zy–Zy† | Male | 84 | 126.29 | 6.42 | <0.001 |
Female | 76 | 121.77 | 5.24 |
†Parameter described by Krogman and Iscan [1] and Buikstra and Ubelaker [20]; as defined in
There was no significant difference (
Comparison between AutoCAD and digital caliper measurements using an independent
Parameters | Methods | N | Mean | SD | |
---|---|---|---|---|---|
OrH† | AutoCAD | 160 | 33.30 | 1.96 | |
Calipers | 160 | 33.33 | 1.97 | 0.91 | |
D-Ec† | AutoCAD | 160 | 37.11 | 2.65 | 0.78 |
Calipers | 160 | 37.19 | 2.74 | ||
NL | AutoCAD | 160 | 22.93 | 2.75 | 0.99 |
Calipers | 160 | 22.93 | 2.76 | ||
ENOH† | AutoCAD | 160 | 25.71 | 3.72 | 0.97 |
Calipers | 160 | 25.72 | 3.72 | ||
APMH† | AutoCAD | 160 | 17.19 | 2.90 | 0.97 |
Calipers | 160 | 17.21 | 2.88 | ||
Zy–Zy† | AutoCAD | 160 | 124.18 | 6.35 | 0.96 |
Calipers | 160 | 124.14 | 6.29 |
†Parameter described by Krogman and Iscan [1] and Buikstra and Ubelaker [20]; as defined in
Evaluating intraobserver error using a paired
Parameter | n | First measurement | Second measurement | Intraobserver error | ||
---|---|---|---|---|---|---|
Mean | SD | Mean | SD | |||
OrH | 30 | 33.82 | 1.92 | 33.84 | 1.96 | 0.84 |
D-Ec | 30 | 38.05 | 2.22 | 38.00 | 2.18 | 0.17 |
NL | 30 | 24.00 | 3.13 | 24.13 | 3.19 | 0.22 |
ENOH | 30 | 27.18 | 3.86 | 27.19 | 3.86 | 0.11 |
APMH | 30 | 23.90 | 6.45 | 24.91 | 8.82 | 0.32 |
Zy–Zy | 30 | 124.62 | 6.15 | 121.30 | 19.96 | 0.33 |
OrA | 30 | 1034.18 | 101.13 | 1030.74 | 101.50 | 0.40 |
OrP | 30 | 115.78 | 6.05 | 116.06 | 6.01 | 0.17 |
ENOA | 30 | 563.44 | 80.40 | 563.91 | 80.78 | 0.29 |
ENOP | 30 | 88.52 | 7.11 | 88.46 | 7.10 | 0.32 |
ENOP | 30 | 666.14 | 96.17 | 666.16 | 96.17 | 0.22 |
ZaA | 30 | 694.32 | 109.64 | 694.30 | 109.62 | 0.34 |
ZaP | 30 | 143.41 | 9.72 | 143.32 | 9.57 | 0.37 |
GBA | 30 | 955.06 | 167.50 | 955.08 | 167.52 | 0.54 |
GBP | 30 | 207.17 | 20.39 | 207.20 | 20.33 | 0.33 |
Logistic regression analysis created a linear regression equation for calculating the logistic regression score (
By using AutoCAD
By using digital calipers
The probability (
The result of the logistic regression analysis is presented in
Sex classification accuracy of craniometry determined using logistic regression analysis
Methods | Sex | Male | Female | Overall | |||
---|---|---|---|---|---|---|---|
n (84) | % | n (76) | % | N (160) | % | ||
AutoCAD | Male | 78 | 92.9 | 6 | 7.1 | 149 | 93.1 |
Female | 5 | 6.6 | 71 | 93.4 | |||
Calipers | Male | 75 | 89.3 | 9 | 10.7 | ||
Female | 4 | 5.3 | 72 | 94.7 | 147 | 91.9 |
Identification of sex from human skeletal remains is essential in forensic investigation. The present study attempts to predict sex from 15 parameters of the cranium using craniometry, and 11 newly developed parameters, i.e., NL, ENOH, APMH, OrA, OrP, ENOA, ENOP, ZaA, ZaP, GBA, and GBP.
From the results shown in
For the parameter APMH, no significant differences were found between men and women, and this may be because of the lack of muscle attachment to bones in the nasospinale– prosthion region. This result was similar for the chin height and symphysis menti, which is a part that rarely varies when compared to the other parts of the jaw [3]. APMH is also one part of the maxillary intermaxillary suture, which is associated with the development of the musculoskeletal system. Most parameters, such as bizygomatic breadth, have significant differences between the sexes and can be used to determine sex with high accuracy and a high degree of sexual dimorphism [4, 12]. This significance may be due to the attachments of the masseter, zygomaticus major, and zygomaticus minor muscles at the points of the landmark.
When comparing the values derived from the present study with those from previous studies, we found that D-Ec and Zy–Zy indicated sexual dimorphism is similar to that found in previous studies [11, 14], while OrH (
A study made use of the parameters of the mastoid process to predict sex, which were modified from the paper by Paiva and Segre [21] by using the AutoCAD method based on scale references to calculate the mastoid triangle area. This suggests that the mastoid process is a good process for sex identification. The present study found a high accuracy (77.5%) of sex prediction for the MTA, while Paiva and Segre [21] – by the Xerographic copy method – reported overlapping values of 60.0% for the right side, 51.67% for the left side, and 36.67% for the total area. Kemkes and Globel [24] presented an accuracy rate of 58.8% for MTA in a German sample, 66.0% in a Portuguese sample, and 65.0% in the combined sample by the digital caliper method.
In 2011, AutoCAD was applied to determine the sex of Thai skeletal remains by using the frontal bone [19]. It was appropriate to investigate these parameters although those for the zygomatic angle were inappropriate [25]. Nevertheless, the present study found that AutoCAD software could be applied to craniometry with high prediction accuracy in the work of forensic anthropology using the sacral base and acetabular rim [17, 18].
Logistic regression analysis of the AutoCAD method displayed an overall sex classification accuracy rate of 93.1%. The digital caliper method showed 91.9% sex classification accuracy rate. The percentage accuracy in this study leans toward higher rates, compared to other studies on Thai populations, which found 90.6% accuracy [15] and studies on other populations such as white South Africans, which found an accuracy of 85.7% from the crania [4]; 80.8% accuracy among black South Africans [11], and 88.2% accuracy among Cretans [12], in predicting the sex correctly. However, the percentage accuracy of sex prediction by statistical analysis is dependent on sexual dimorphism. The number of parameters and samples are also important. The study by Iscan and Steyn [10] used 13 crania and 4 mandible parameters to predict sex, and the sample sizes of men and women were equal, showing a high accuracy rate of 97.8% using the crania. In the present study, 15 parameters of 84 men, and 76 women were used.
This study used an AutoCAD method with digital photographs. This method was convenient and durable for reassessment and took less time to reset the point of landmark to measure the area and perimeter dimensions of the crania. Moreover, this method could examine each position, which may be away from the skeletal line, and expand it using an automatic method for 3D digital skull construction [26]. Caliper measurement may be difficult to reevaluate, and to sustain landmark points in the case of bone loss or fracture may also be difficult.
The accuracy of the AutoCAD measurements was also assessed. The study showed no significant difference between the AutoCAD measurement, which was measured from the digital photograph, and the digital caliper measurement, which was taken directly on the crania. In addition, the test for intraobserver error from AutoCAD reassessment showed that there was no significant difference between measurements made at the first and second time points, suggesting that the AutoCAD method is sufficiently accurate to be used for sex determination. Moreover, in the application of the AutoCAD method, one should be aware of the plane of reference setting for photography.
The determination of sex from Northern Thai crania using AutoCAD and conventional caliper methods examined in the present study shows high accuracy for both methods and is suggested for use to predict sex from skeletal remains.