Binary Logistic Regression Analysis of Foramen Magnum Dimensions for Sex Determination

Abstract

Purpose. The structural integrity of foramen magnum is usually preserved in fire accidents and explosions due to its resistant nature and secluded anatomical position and this study attempts to determine its sexing potential. Methods. The sagittal and transverse diameters and area of foramen magnum of seventy-two skulls (41 male and 31 female) from south Indian population were measured. The analysis was done using Student's t-test, linear correlation, histogram, Q-Q plot, and Binary Logistic Regression (BLR) to obtain a model for sex determination. The predicted probabilities of BLR were analysed using Receiver Operating Characteristic (ROC) curve. Result. BLR analysis and ROC curve revealed that the predictability of the dimensions in sexing the crania was 69.6% for sagittal diameter, 66.4% for transverse diameter, and 70.3% for area of foramen. Conclusion. The sexual dimorphism of foramen magnum dimensions is established. However, due to considerable overlapping of male and female values, it is unwise to singularly rely on the foramen measurements. However, considering the high sex predictability percentage of its dimensions in the present study and the studies preceding it, the foramen measurements can be used to supplement other sexing evidence available so as to precisely ascertain the sex of the skeleton.

Figure 1

The base of the skull showing the sagittal dimension (S) and transverse dimension (T) of the foramen magnum.

Figure 2

The values of sagittal diameter (mm) revealed a high interindividual variability.

Figure 3

The values of transverse diameter (mm) revealed a high interindividual variability.

Figure 4

The Q-Q plot of sagittal diameter shows normal distribution.

Figure 5

The Q-Q plot of transverse diameter shows normal distribution.

Figure 6

ROC curve for the predicted probabilities of sagittal diameter.

Figure 7

ROC curve for the predicted probabilities of transverse diameter.

Figure 8

ROC curve for the predicted probabilities of area using Radinsky's formula.

Figure 9

ROC curve for the predicted probabilities of area using Teixeria's formula.

Figure 10

A moderately positive correlation between the sex-pooled sagittal and transverse diameter (mm) of the foramen magnum (r = 0.549, p < 0.001).

Figure 11

It depicts the ethnic variability of the foramen magnum dimensions in millimetres in different ethnic groups. Most of the values are obtained from a study by Martin, 1928 [17], and Nakashima, 1986 [10]. The data below shows the regions represented by the numbers. ^∗A study by Gruber et al., 2009 [6]. ^∗∗A study by Raghavendra Babu et al., 2012 [9]. The numbers 37 and 38 represent the present study in males and females, respectively. 1 = Germans m, 2 = Swiss f, 3 = Elsasee m, 4 = Elsasee f, 5 = Romans m, 6 = Romans f, 7 = Tyrolese, 8 = Bavarians m, 9 = Romans f, 10 = Swiss Wallis m, 11 = Swiss Wallis f, 12 = Swiss-Danis, 13 = Ainos m, 14 = Ainos f, 15 = Japanese m, 16 = Japanese f, 17 = Bashkirs m, 18 = Telengets, 19 = Chinese, 20 = Buryats, 21 = Torguts, 22 = Malays m, 23 = Malays f, 24 = Australians m, 25 = Australians f, 26 = Paltacalos m, 27 = Paltacalos f, 28 = Middle Kyushites m, 29 = Kantoites m, 30 = North Kyushites m, 31 = Yoron Islander/Fuschen Chinese, 32 = Kikai Islanders m, 33 = Shlingol Mongolians m, 34 = Central Western Europe^∗, 35 = Indian male^∗∗, 36 = Indian female^∗∗, 37 = Indian male (present study), and 38 = Indian female (present study).