Cerezo-Roman and Hernandez 2014

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Forensic Anthropology Population Data

Estimating age at death using the sternal end of the fourth ribsfrom Mexican males

Jessica Ines Cerezo-Roman a,b,*, Patricia Olga Hernandez Espinoza c

a Pima County Medical Examiner Forensic Science Center, 2825 E. District Street, Tucson, AZ 85714, USAb School of Anthropology, The University of Arizona, 1009 E. South Campus Drive, Tucson, AZ 85721-0030, USAcCentro INAH Sonora, Jesus Garca final s/n, Col. La Matanza, Hermosillo, Sonora 83000, Mexico

1.

Introduction

Estimation of biological age-at-death is one of the moreimportant parts of the analysis of modern and ancient human

skeletal remains. For adults, age-at-death estimates frequentlyutilize multiple indicators that reflect standard processes of bonedeposition, remodeling, and reabsorption that occur throughoutthe life of an individual. However, these processes are affected and

influenced by numerous genetic, environmental, and culturalfactors. Taking these into consideration, the selection of appropri-ate methods for estimating age needs to be informed by method-specific data on the margins of error for each target sample.

Skeletal maturationprocesses provide abasis for estimating theage of a skeleton. In younger subadults, the estimation of ageusually relies on bone and tooth maturation. However, there aresubstantial variations in the timing of these developmentalchanges among different individuals, even those who do not

suffer from any major growth disruptions and/or stress episodes[1,2]. With mature adults, estimations of age-at-death are mainlyderived from evaluating degenerative processes usually caused by

normal wear and tear on the body over time. Researchers have

observed

and

analyzed

these

changes

in

specific

skeletal

samplesand theyhavedeveloped classificationmethods to estimate group-specific age-at-death (for a summary and discussion of thesemethods and techniques see references [26]). These degenerative

processes also reflect an individuals life history of growthdevelopment and genetic predisposition. Considering this, it islikely that degenerative changes will differ in timing and manneramong different populations. Taking into consideration an

individuals life history of growth, development, lifestyle, andgenetic predisposition, researchers argued for critically evaluatingexisting methods that estimate the age-at-death among differenpopulations [710]. Several studies have concluded that it is

essential toassess the accuracyof and, ifnecessary,modify existingmethods to more effectively estimate the age-at-death oindividuals from different populations around the globe [e.g., 710]. These types of studies are very useful as they facilitate theprocess of adjusting existing methods to specific populations and

of acquiring a deeper andwider understanding of human variationMost standards used to estimate age-at-death were developed

with samples from North America, such as the Terry collection at

the Smithsonian Institution in Washington, D.C., the HamannTodd collection in Cleveland, Ohio, and individuals from theKorean War, among others [11]. These collections are primarilycomposed of Americans with Northern European and African

ancestry. Individuals in these collections had very different lifestyles and genetic heritages than Latin American populations. Thisresearch evaluates the applicability of methods developed to

Forensic Science International xxx (2014) xxxxxx

A R T I C L E I N F O

Article history:Received 30 April 2013

Received in revised form 21 September 2013

Accepted 30 December 2013Available online xxx

Keywords:

Forensic science

OsteologyAge estimation

Sternal end of the ribs

Mexican population

A B S T R A C T

The indicators proposed by Iscan et al. (1984) are said to reflect age changes thatoccurin the sternal endof the fourth rib. These indicators have been used to estimate age-at-death in adult skeletal samplesHowever, Iscan et al. developed their methods using a forensic sample from Florida (U.S.A.). In order t

test thereproducibility of those methodswe evaluate its accuracy for the fourth ribs by applying it tosample of known age and sex but of different biological affinity: modern males from Mexico City. Wfound that the method developed by Iscan et al. underestimates age-at-death in the Mexican sample

Published by Elsevier Ireland Ltd

* Corresponding author at: Pima County Medical Examiner Forensic ScienceCenter, 2825 E. District Street, Tucson, AZ 85714, USA. Tel.: +1 520 248 5856.

E-mail addresses: [email protected] (J.I. Cerezo-Roman),

[email protected] (P.O. Hernandez Espinoza).

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FSI-7475; No. of Pages 6

Please cite this article in press as: J.I. Cerezo-Roman, P.O. Hernandez Espinoza, Estimating age at death using the sternal end of thefourth ribs from Mexican males, Forensic Sci. Int. (2014), http://dx.doi.org/10.1016/j.forsciint.2013.12.044

Contents lists available at ScienceDirect

Forensic Science International

journal homepage: www.elsev ier .com/loc ate / fo rsc i int

0379-0738/$ see front matter. Published by Elsevier Ireland Ltd.

http://dx.doi.org/10.1016/j.forsciint.2013.12.044


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Changes in the sternal end of the fourth ribs were evaluatedbased on morphologic and metric characteristics of the costochon-

dral cavity, particularly the depth, shape, and wall and rimconfigurations without prior knowledge of the known age of theindividual. Measurements and observations used in this researchfollowed the procedures of Iscan et al. [12] who divided these data

into three componentswith each component comprising a series ofstages (Table 2). The pit depth was measured with a depth calipercalibrated to 0.1 mm. The caliper was held perpendicular to thebase of the pit and the measurement was taken where the distance

between the base of the pit and the adjacent anterior or posteriorwall was the greatest. The method stages are a progression fromzero to five where stage zero represents ribs that have justcompleted maturation processes and are fully developed. Stage

one represents the beginning of degenerative changes andsubsequent stages represent increasing degenerative changes(e.g., young adults should be closer to stages 0 and 1 while olderadults should be at stages 4 or 5) (see Table 2).

3. Results

Statistical analyses were performed using the softwareprograms SPSS 16.0 and Microsoft Excel 2007. Analytical

evaluations included descriptive statistics, one-way analysis ovariance (one-way ANOVA), and analysis of bias and inaccuracies

The sample presents a known age mean of 49.58 and a standarddeviation (SD) of 18.807. This sample presents a slight kurtosistoward older ages (Table 3). In order to understand better how therelationships between the components and the different stages in

the Mexican sample comparisons were made between the meanknown ages and the stages of each component (Table 4) and thesewere compared with similar analyses using the fourth rib from theyounger sample evaluated by Iscan et al. [12]. Table 4 lists the

descriptive statistics of the males in our Mexican sample and fromIscan et al. [12]. In our Mexican sample, changes associated withtheprocess of agingbegan tomanifest in ribs three and four arounda mean age of 44 years old (Table 4). This result contrasts with

those of Iscan et al. [12], inwhich the components and initial stagespresent at mean age of 20.3 years (Table 4). When the mean datafor the fourth ribs of theMexican sample are compared to themean

age of Iscan et al. [12], the Mexican sample means are older in al

phases of the components.The second statistical analysis was a one-way analysis o

variance (One-factor ANOVA) (Table 5). This analysis describes

variance in the pit depth (component one), pit shape (componenttwo), rim and wall configurations (component three), anddependence of variance in the known age based on comparisonof themean values. ANOVA did not reveal a significant relationship

between known age and the fourth rib pit depth (Table 5). The pitshape reveals a level of 0.06, and, therefore there is no statisticasignificance between the known age and the pit shape (Table 6)However, rim and wall configurations (component 3) have a

significant relationship (P = 0.01) with the known age (Table 7).The analysis of bias and inaccuracy (Table 8) were made

following current studies such as Hens et al. [9], Saunders et al. [8]

and Santos [44]. The bias is the mean over- or under-predictionS(estimate age known age)/n, where n = the number of casesThe inaccuracy is the average absolute error of age estimationwithout reference to over- or under-prediction, Sjestimateage known agej/n. The means were estimated as the mid-point

of age category ranges except for the last open-end category where61 was used. The results of the analysis of bias and inaccuracyreveal that the degree of bias and inaccuracy generally is higher asage increments.There isa lowerbias inageestimationup toage30

There is a shift from slight underestimation of age to a higherdegree of underestimation after age 40. Age estimations over age60 are dramatically underestimated. Fig. 1 graphically displays theresults of known age and estimated age. Each individual is plotted

on the graph so that the degree of bias and inaccuracy may be

visualized.

Bias

and

inaccuracy

in

this

study

were

then

compared

Table 1

Known age ranges.

Age ranges Male

2130 years 14

3140 years 12

4150 years 155160 years 7

61+ 23

Total 71

Table 3

Known age descriptive statistics.

Real chronological age

N Valid 71

Missing 0

Mean 49.58

Std. error of mean 2.232

Median 45.00Mode 25a

Std. deviation 18.807

Variance

353.705Skewness .384

Std. error of skewness .285

Kurtosis .813

Std. error of kurtosis .563

Range 77

Minimum 21

Maximum 98Sum 3520

a Multiple modes exist. The smallest value is shown

Table 2

Iscan et al. [12] components and stages.

Component 1: Pit depth

0. Flat to slightly billowy extremity with no indentation (pit) 1.1mm.

1. Definite pit formation with a depth ranging from 1.1 to 2.5mm.

2. Pit depth ranging from 2.6 to 4.5mm.

3. Pit depth ranging from 4.6 to 7.0mm.4. Pit depth ranging from 7.1 to 10.0mm.

5. Pit depth 10.1mm.

Component 2: Pit shape

0. Juveniles and adolescents with no pit formation at the

flat or billowy articular surface.

1. A shallow, amorphous indentation (pit) is present.

2. Formation of a V-shaped pit with thick walls.

3. Pit assumes a narrow U-shape with fairly thick walls.4. Wide U-shaped pit with thin walls.

5. Pit is still a wide U-shape, yet deeper, more brittle, and

poorer in texture with some disintegration of bone.

Component 3: Rim and wall configuration

0. Specimens with a smooth regular rim and no wall formation.

1. Walls becoming apparent with a thick, smooth regular rim.

2. Definitely visible thick and smooth walls with a scalloped or slightly

wavy rim.

3. A transitional stage between the regularity of Stage 2 and irregularityof Stage 4. Scalloped edges are disappearing and walls are thinning, yet

walls remain fairly sturdy without significant deterioration of

bone texture.4. Rim becomes sharper and increasingly irregular with more frequent

bony projections, often most pronounced at the cranial and caudal

margins of the rib. Walls show further thinning and are less

sturdy with noticeable deterioration in texture.

5. The texture shows extreme friability and porosity. Rim is very

sharp, brittle, and highly irregular with long bony projections.

Occasionally, as the depth of the pit increases, openings form

in areas where walls are incomplete.

J.I. Cerezo-Roman, P.O. Hernandez Espinoza/Forensic Science International xxx (2014) xxxxxx 3

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with the sternal end of rib bias and inaccuracy from the study ofSaunders et al. [8] (Table 8). Saunders et al. [8] presented a blindtest of four morphological methods of adult age-at-deathestimation using a sample from a 19th century Canadian

pioneer cemetery. Among the methods that they used is thesternal end of the ribs, and they mention that the sample variedfrom 27 to 49 individuals. However, in their article the sample

number is not presented and for this reason it is not presented in

Table 8. Different for Saunders et al. [8] the sample in this studypresent under and over estimation of ages. However, there biaswas lower in the 1729 and 4049 age groups, while in thecurrent study they are slightly higher. In the study of Saunders

et al. [8] there is an increase of bias in age categories older than50 years and an underestimation of ages in individuals olderthan 40 years, both of which are similar findings in the current

study.

Table 4

Fourth rib descriptive statistics.

Components, stages and fourth rib SEMEFO & Tolentino Iscan et al. (1)

N Mean age SD N mean age SD

Component 1: Pit depth

0. Less than 1.1mm

1. 1.12.5mm 6 44 24.44 9 20.3 3.32

2. 2.64.5mm 32 47 17.44 29 30.7 12.403. 4.67.0mm 16 55 17.71 31 40.9 13.72

4. 7.110.0 mm 9 55.0 15.395. 10.1mm or more 4 57.5 12.92

Total 54 49 18.51 82 37.9 16.15

Component 2: Pit shape

0. No pit formation, flat or billowy surface

1. A shallow, amorphous indentation (pit) 4 38 14.52 4 17.3 0.50

2. V-shaped pit with thick walls 12 40 19.62 15 22.8 3.283. Narrow U-shape with fairly thick walls 19 52 17.25 28 30.5 9.61

4. Wide U-shaped pit with thin walls 14 51 16.35 22 47.1 11.61

5. Wide U-shape, and poorer in texture 5 64 19.04 15 61.6 12.94Total 54 49 18.51 84 38.4 17.26

Component 3: Rim and walls configuration

0. Smooth regular rim and no wall formation

1. Beginning walls with a thick, smooth regular rim 3 38 18.93 5 17.8 1.30

2. Visible walls that are thick and smooth with a scalloped or slightly wavy rim 25 44 17.05 25 24.1 3.55

3. Transitional stage 11 46 16.15 20 34.3 11.62

4. The rim sharper and increasingly irregular with more frequent bony projection.The walls show further thinning.

10 63 16.34 16 49.5 11.21

5. Texture shows extreme friability and porosity. 5 62 17.92 16 58.2 11.53Total 54 49 18.51 82 37.8 16.67

Table 5

Known age and component 1 pit depth.

ANOVA


Sum of squares df Mean square F Sig.

Between groups 1035.031 2 517.516 1.541 0.224

Within groups 17,130.302 51 335.888

Total 18,165.333 53

Table 6

Known age and component 2 pit shape.

ANOVAReal chronological age


Between groups 3010.428 4 752.607 2.433 0.06

Within groups 15,154.905 49 309.284

Total 18,165.333 53

Table 7

Known age and component 3 rim and wall configuration.

ANOVA



Between groups 4173.561 4 1043.39 3.654 0.011Within groups 13,991.772 49 285.546

Total 18,165.333 53

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4. Discussion

In this study, age changes related to the sternal end of the riband the method developed by Iscan et al. [12] were examined on awell-documented sample of modern males from Mexico. This was

done by observing the relationship between known age and themorphological changes in this area through descriptive statisticsand one-way statistical analysis of variance (one-way ANOVA).Using the method proposed by Iscan et al. [12], we also evaluated

the bias and inaccuracy between the known and estimated ages.The analysis of descriptive statistics for each phase and

component suggest that as known ages increment the phases ofeach component also increment. However, there is not a clear

delimitation between the known age and component increments.Also, when the current results are compared with those from Iscanet al. [12], the known age changes occurred at older ages in all the

phases and components. The increment in ages in the study of

Iscan et al. [12] are also lower than the results in our study. Also inthe study of Iscan et al. [12] the standard deviations are also lowerthan the results in our study. Oettleand Steyn [37] also performed

a similar study, applying similar procedures on a South Africasample. However, their results were different from both ourinvestigation and from the results of Iscan et al. [12]. In theirsample, the changes that occurred with age occurred at earlier

ages. Yavuz et al. [36] also observed that the degenerativeprocesses were underestimated, particularly before 40 years ofage.

The second analysis performed was a one-way analysis of

variance or one-factor ANOVA. The results from this statistical

analysis revealed that there was a statistically significan

relationship between the known age and the rim and walconfiguration. The results we obtained are different from thosereported by Iscan et al. [12]. The results of Iscan et al. [12] suggestthat all the components had significantvalues,whilewe found tha

rim andwall configurationswere themostdependent on age in oursample. The one-factor ANOVA analysis reveals that differencesexist between known ages and rib components.

The analysis of bias and inaccuracy suggest that ages between

21 and 30 present the lowest biases and inaccuracies. Howeverthese values deviate dramatically after the age of 31, and after theage of60 there is thehighest increase. Itwas found that themethodunderestimates the known ages of individuals. When the bias and

inaccuracy results are compared with other studies, such as theone by Saunders et al. [8], a similar pattern was observed in thegroup ages after 40 years. In the current research and in Saunders

et al. [8] there is anunderestimation of the ages,particularly true in

individuals older than 50 years. Most of the changes observed inthe sternal end of the ribare related todegenerative changeswhichare difficult to interpret and likely show variation related to life-

style, environment and activities [8,9]. Therefore, it is notsurprising that as the individual age biases and inaccuraciesassociated with age estimates also will increase.

This study confirms conclusions of previous studies tha

suggest there are variations between populations around theworld and changes in human remains related to age [9,45]Considering this, it is necessary to continue exploring morpholog-ical variation among populations and differential changes through

time that occur with age to more accurate estimate age-at-deathand to have a broader understanding of human variation.

5. Conclusions

Most research on estimating age-at-death using humanskeleton material suggested that degenerative processes are goodindicators for age estimates. However, these processes can vary

among populations, depending upon factors such as biologicaaffinity and relate to growth and development, as well as life-conditions and lifestyle. The majority of indicators and techniquesused to determine age-at-death by physical anthropologists in the

United States are derived from individuals who are genetically andmorphologically different from Mexican populations.

The objective of this research was to evaluate the precision othe method proposed by Iscan et al. [12] to estimate the age-at

death using the sternal end of the rib on a Mexican sample. We

selected

specimens

from

two

groups

of

known

age

and

sex.

It

was

Fig. 1. Comparison of known age and estimate age for each male.

Table

8Bias and inaccuracies for the Iscan et al. sternal end of the rib estimates.

N Bias Inaccuracies

Known age this study

2130 14 6.8 8.2

3140 12 11.5 12.6

4150 15 9.3 10.4

5160 7 8.7 12.2

60+ 22 12 18.7

Saunders et al. [8]

Sternal end of ribs known age

1729 0.8 5.0

3039 11.1 11.1

4049 2.5 7.1

5059 9.1 9.1

60+ 15.5 16.6

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