Nasal anthropometry is concerned with the measurements of the proportions, size and shape of the human nose. By applying anthropometric methods, it has become possible to quantify diversity of human phenotypes and specific features that differentiate individuals and ethnic groups (Farkas et al., 2005; Franco et al., 2013) . The nasal indices are among the most important cephalometric parameters useful in inter-racial and intra-racial morphological classification and categorization. They are useful in the description of the nasal morphological characteristics of human population in different geographical location. Based on the nasal index, there are three categories of nose namely: leptorrhine (nasal index ≤ 69.9); mesorrhine (nasal index 70 - 84.9) and platyrrhine (nasal index ≥ 85) (Williams et al., 1995) .
Anthropologists have used nasal indices in many ethnic groups for categorization and gender discrimination (Anas, 2010; Jimoh et al., 2011; Omotoso et al., 2011; Oludiran et al. 2012; Eliakim-Ikechukwu et al., 2012; Eliakim-Ikechukwu et al., 2013; Ogah et al., 2014; Oria et al., 2018) . Extensive literature search revealed paucity of published studies on facial anthropometry of Tiv and Idoma people of Benue State. The Tiv people are said to be of Bantu origin from the Central African continent, in the Shaba area of the present Democratic Republic of Congo (Shii, 2011) , while the Idoma people reportedly migrated from Apa in Kwararafa Kingdom after her disintegration (Udo, 1970) . These two ethnic groups constitute the major population blocks in Benue state of north-central Nigeria. The state derives its name from River Benue, the second largest river in the country and the most prominent geographical feature in the state. Its geographical coordinates are longitude 7˚47' and 10˚0' east, latitude 6˚25' and 80˚8' and it shares boundaries with five other states namely: Nasarawa to the north, Taraba to the east, Cross river to the south, Enugu to the south-west, and Kogi the west. The state also shares common boundaries with Cameroun on the south-east. Benue has a population of 4,780,389 (2006 census) and occupies a land mass of 32,518 square kilometres (Oria et al., 2018) .
This study was, therefore, done to describe the nasal morphological characteristics and indices of the two ethnic groups. The observations and findings of this study would possibly provide platforms for similar extended studies in other ethnic groups for comparison and categorization.
2. Subjects and Methods
The study was carried out in Makurdi from May to November, 2015. A cross sectional sample of 600 subjects (300 Tiv and 300 Idoma with half of the subjects in each ethnic group being males and the remaining being females) was randomly selected for the study. Participants were informed of the procedure and purpose of the study and written informed consent was obtained from each participant. Demographical data including age, local government of origin, ethnicity, duration of stay in the land of origin, parental and grandparental origin was taken. Subjects within the age range of 18 - 32 years were selected for this study. The subjects were made to sit comfortably on a chair with the head held out straight in the anatomical position. Nasal length and nasal width were measured in centimetres using vernier calliper from which nasal index was later calculated. Each measurement was taken twice and the average obtained.
2.1. Anthropometric Landmarks
The measurements were taken with standard anthropometric instrument (vernier callipers) using recognized skeletal landmarks according to Ross and Marfell-Jones (1991) as follow:
1) Nasion: The point on the root of the nose where the mid-saggital plane cuts the naso-frontal suture.
2) Nasospinale: The lowest point on the inferior margin of the nasal aperture as projected in the mid-saggital plane.
2.2. Measurement Technique
1) Nasal Length: Distance from nasion to nasospinale. With the subject sitting on a chair in relaxed mood and the head in anatomical position, a verniercalliper was used to take this measurement to the accuracy of 0.1 cm.
2) Nasal Breadth: Distance from ala to ala (interalar distance), measured at right angle to the nasal height. With the subject sitting on a chair in relaxed mood and the head in anatomical position, a verniercalliper was used to take this measurement to the accuracy of 0.1 cm.
Nasal Index (NI) was calculated according to Williams et al. (1995) as nasal breadth/nasal height × 100.
2.3. Inclusion Criteria
The subjects considered for this study all belonged to either Tiv or Idoma ethnic group with two generations of indigenization. They were born and brought up in Nigeria to harmonize effects of environmental factors on the subjects. The subjects were healthy individuals free from any apparent nasal deformity.
2.4. Exclusion Criteria
Subjects who did not meet the inclusion criteria, specifically, those that did not belong to Tiv or Idoma ethnic groups, those below or above the stipulated age range, those with nasal trauma and those not willing to participate were excluded from the study.
2.5. Ethical Approval
In line with the Helsinki Declaration of 1975, as revised in 2000, ethical approval was obtained from Ahmadu Bello University Health Research Ethics Committee (HREC). The objectives of the study were explained to the subjects and only those who gave informed consent were included in this study.
2.6. Data Analysis
The statistical methods used to analyze the data included: 1) Descriptive statistics to describe measurement data such as means and standard deviations (SD). 2) Student t-test to compare mean values in males and females of the two ethnic groups. All data were analyzed using a statistical package SPSS for windows version 20 (IBM Corporation, New York, USA). Statistical significance was considered at p ≤ 0.05.
Six hundred (600) subjects were recruited for this study; three hundred (300) each from the two ethnic groups. From each ethnic group, half of the number (150) was males and the remaining half (150) was females. The age of this sample ranged from 18 - 32 years. The mean age of the study sample was 24.3 ± 3.5 years with a mean of 25.1 ± 3.6 years and 23.4 ± 3.1 years for male and female subgroups respectively. The age difference between the sexes was statistically significant (p < 0.05). The Tiv ethnic group had mean age of 25.5 ± 3.7 years for male and 24.0 ± 3.1 years for female subgroups respectively, while the Idoma ethnic group had mean age of 24.7 ± 3.5 years for male and 22.8 ± 3.0 years for female subgroups respectively.
The mean nasal length of male and female Tiv subjects was 4.6 ± 0.65 cm and 4.1 ± 0.51 cm respectively while the mean nasal breadth was 4.5 ± 0.58 and 3.9 ± 0.44 cm respectively. The mean nasal index in male and female Tiv subjects was 97.7 ± 11.85 and 93.6 ± 9.63. Thus the Tiv sample exhibited sexual dimorphism with respect to nasal length, nasal breadth and nasal index with males having higher mean values than females and the differences were statistically significant as shown in Table 1.
The mean nasal length in male and female Idoma subjects was 4.5 ± 0.74 cm and 4.0 ± 0.49 cm respectively while the mean nasal breadth was 4.2 ± 0.59 cm
Table 1. Descriptive statistics for nasal length, nasal breadth and nasal index of tiv ethnic group.
p ≤ 0.05.
and 3.6 ± 0.47 cm respectively. The mean nasal index in male and female Idoma subjects was 94.4 ± 11.19 and 90.3 ± 10.51. Thus the Idoma sample exhibited sexual dimorphism with respect to nasal length, nasal breadth and nasal index with males having higher mean values than females and the differences were statistically significant as shown in Table 2.
The mean nasal length of Tiv was 4.4 ± 0.63 cm and that of Idoma was 4.3 ± 0.67 cm. The mean nasal breadth of Tiv was 4.2 ± 0.59 cm and that of Idoma was 3.9 ± 0.61 cm. The mean nasal indicex of Tiv was 95.7 ± 10.97 and that of Idoma was 92.3 ± 11.03. Whereas no statistical difference existed in the mean nasal length of the two ethnic groups (p = 0.072), there was statistically significant mean difference in nasal breadth (p = 0.001) and nasal index (p = 0.001) with Tiv having higher mean values as shown in Table 3. Table 4 shows the classification of nose type according to nasal index in the two ethnic groups.
Table 2. Descriptive statistics for nasal length, nasal breadth and nasal index of idoma ethnic group.
p ≤ 0.05.
Table 3. Descriptive statistics of the study parameters according to ethnicity.
p ≤ 0.05.
Table 4. Classification of nose type according to nasal index of Tiv and Idoma ethnic groups.
The mean nasal index of Tiv males and females, from this study, was 97.7 and 93.6 respectively with a combined index of 95.7. Similarly, the mean nasal index (NI) of Idoma males and females was 94.4 and 90.3 respectively with a combined nasal index (CNI) of 92.3. It was, therefore, observed that the predominant nasal type among both ethnic groups, based on NI, was platyrrhine or broad nose. The result of the present study agreed with those from other studies about Nigerian ethnic groups having platyrrine nose (Oladipo et al., 2010; Omotoso et al., 2011; Jimoh et al., 2011; Oludiran et al., 2012; Eliakim-Ikechukwu et al., 2012, 2013; Ogah et al., 2014; Oria et al., 2018) . The studies cited above were conducted on one or the other of Omoku, Bini, Ibo, Ibibio, Yakurr, Yoruba, Idoma and Fulani ethnic groups of Nigeria. In contrast, in a study conducted by Anas (2010) on students of Bayero University Kano in Northern Nigeria, it was observed that Hausa females’ nasal index value was less than 69.9 (leptorrhine) whereas that for the males was greater than 70 (mesorrhine). According to Abraham and Romo (2006) and Risley and Crooke (1915) respectively as in Jimoh et al. (2011) , most Western Europeans have leptorrhine nasal morphology with long and narrow nose with a nasal index of 69.9 or less; the Bantus and Bushmen of South Africa as well as indigenous aboriginals in Australia have platyrrhine nose with broad nose with nasal index of 85.0 and above. Race, tribe and climatic conditions are variables that determine the shape of the nose. Narrower noses are said to be favoured in cold and dry climates while broader noses in warmer and moister ones as a consequence of natural selection in human evolution.
Sexual dimorphism, a condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs, was apparent in our study. Nasal length, nasal breadth and nasal index showed sexual dimorphism in the two ethnic groups with males having significantly higher mean values than females and this is consistent with findings of other researchers (Anas 2010; Oladipo et al., 2010; Omotoso et al., 2011; Jimoh et al., 2011; Oludiran et al., 2012; Eliakim-Ikechukwu et al., 2012, 2013; Ogah et al., 2014; Oria et al., 2018) . According to Farkas and Munro (1986) the nasal index is related to regional and climatic differences. It would be expected that ethnic groups in the same climatic region should not have much difference in their nasal indices. It then appears that the uniqueness of the nose exists in geographical clusters and may be determined by the environment interacting with genetic constitution.
The mean nasal height values obtained in our study (4.6 ± 0.65 cm and 4.1 ± 0.51 cm for male and female Tiv subjects; 4.5 ± 0.74 cm and 4.0 ± 0.49 cm for male and female Idoma subjects) were lower than the values obtained from previous research on Idoma (4.9 ± 0.18 in males and 4.8 ± 0.11 in females) (Oria et al., 2018) ; Bini (4.7 ± 0.11 cm in males and 4.6 ± 0.14 cm in females) (Omotoso et al., 2011) ; Yoruba (4.6 cm), Hausa (4.7 cm) and Fulani (4.7 cm) (Ogah et al., 2014) . Our values were comparable to those of Ibo (4.3 cm) (Ogah et al., 2014) ; Ibibio (4.1 cm in males and 3.8 cm in females) and Yakurr (4.0 cm in males and 3.6 cm in females) (Eliakim-Ikechukwu et al., 2013) . In adult Chileans, the mean nasal length is 5.0 cm and 4.7 cm in males and females (Troncoso et al., 2008) . In a study on an Indian population, Kaushal et al. (2013) summed that Brahmin males had nasal length of 47.59 mm, Muslims had nasal length of 45.88 mm and Majhabi-Sikhs had nasal length of 44.64 mm while in case of females, the sequence was Brahmins (44.09 mm) followed by Majhabi-Sikhs (41.41 mm) and Muslims (39.36 mm).
From the findings of this research and based on nasal index, Tiv and Idoma ethnic groups had platyrrhine nose. They also showed sexual dimorphism of their nasal length, nasal breadth and nasal index with males having significantly higher mean values than females. This study will provide additional baseline data which will be valuable in physical anthropology and in clinical practice for aesthetic or reconstructive surgery and also for forensic investigations.