References
FemurSubtrochantericShapeandAncestryAssessmentinModernJapaneseandThaiIndividuals*
SeanD.Tallman,DepartmentofAnthropology,UniversityofTennessee,Knoxville,TN,[email protected]
Introduction
Thepaucityofcranialremainspresentsasignificantproblemtobioarchaeologists andforensicanthropologistsinthedeterminationofancestry.Whilepostcranialancestrymethodsgenerallylacktheaccuracyattainedfromcranialmethods,morphoscopicandmorphometricapproacheshavebeenappliedtotheproximal,diaphyseal,anddistalfemurwithvaryingsuccess.Notably,femursubtrochantericsizeandshapehavebeenemployedtodifferentiatebetweenbroadancestralgroupsusinganterior-posterior(A-P)andmedial-lateral(M-L)sectioninglines(GilbertandGill1990;GillandRhine1990),inadditiontotheplatymericindex(PI;Wescott2005).ThePIiscalculatedbydividingtheA-PbyM-Lsubtrochantericdiameterandmultiplyingby100,withindividualsexhibitingplatymeric(medio-laterallybroad;PI≤84.9),eurymeric(rounded;PI85.0- 99.9),orstenomeric(antero-posteriorlybroad;PI≥100.0)subtrochantericregions(Fig.1).WhilethetraditionalsectioninglinepositionsandPIthresholdsarepopulationdependent,theyachievesuccessratesinexcessof80%whendifferentiatingbetweenNativeAmericans(generallyplatymeric)andpooledAfro- andEuro-Americans(generallyeurymeric).ThoughitisoftenassumedthatEastAsiangroupsalsoexhibitsimilarlyplatymericsubtrochantericmorphologies,thisassumptionisbasedmainlyondataderivedfromNativeAmericanarchaeologicalassemblages.However,recentworkhasdemonstratedthatsomeEastAsiangroupsarelessplatymericthanNativeAmericans(TallmanandWinburn2015),whilesomeEasternEuropeanpopulationsexhibitunexpectedlyhighratesofplatymeria(McIlvaine andSchepartz 2015).Assuch,population-specificsubtrochantericancestrymethodsshouldbeused.
Figure1.Crosssectionsofplatymeric(a),eurymeric(b),andstenomeric(c)femora(TallmanandWinburn2015).
Severalmethodologicalissuesandinherentassumptionshavebeenidentifiedwiththeuseoftheproximalfemurinancestryassessment.Inparticular,theA-PandM-Lsubtrochantericmeasurementsgenerallyexhibithighintra- andinter- observererrorrates(AdamsandByrd2002).Further,subtrochantericmethodsassume:thatthereisminimalsexualdimorphismwithinpopulations;thatpopulationsaretemporallyandgeographicallyhomogenous;andthatpopulationdifferencesinsubtrochantericformareattributabletogeneticvariationratherthanbiomechanicalstress(WescottandSrikanta 2008).WhileWescottandSrikanta foundthatdimorphism,intrapopulation variance,andbiomechanicalstressesdoaffectsubtrochantericform,thesefactorsdonotsignificantlyimpedediscriminatingbetweenNativeAmericanandAfro-/Euro- Americanindividuals.
ThecurrentstudyfurtherexploresfemursubtrochantericsizeandshapevariabilityanditsuseinforensicancestryassessmentbytestingWescott’s (2005),GillandRhine’s(1990),andTallmanandWinburn’s (2015)femursubtrochantericmethodsandassociatedassumptionsonmodernJapaneseandThaiindividualsaged17-96years.
TheJapanesesampleconsistsof 287 knownindividualsfromthegreaterTokyoregionwhodiedduringthelate19th/early20thcenturies(ChibaUniversity)andthosewhodiedduringthe1960s/1970s(JikeiUniversity).TheThaisampleiscomposedof149 knownindividualsfromnorthernThailandwhodiedinveryrecentdecades(KhonKaenUniversity).AEuro-Americansampleof77malesidentifiedbytheDepartmentofDefensewasusedtohelptestthediscriminatorypowerofsubtrochantericsizeandshape.Toexamineintra- andinter- observererrorrates,45Chibafemorawerere-measured;toexaminetheeffectsofbodysize,femurmaximumlength(FML)andmaximumfemoralheaddiameter(MHD)weremeasuredforasubsampleof136Thaiindividuals.Intraclasscorrelationcoefficients,discriminantfunctions,descriptivestatistics,t-tests,andANOVAswerecalculatedintheSPSSstatisticalsoftwarepackage.
MaterialsandMethods
Sample N MeanPI SD PIRange Platymeric Eurymeric Stenomeric
Japanesefemales 70 80.211,2 6.45 57.44-99.22 T:80.0%4
A: 90.0%T:20.0%A:10.0%
T: 0%A:0%
Japanesemales 217 82.161,3 7.43 55.65-103.72 T: 62.7%4
A:79.7%T:35.9%A:20.3%
T:1.4%A:0%
Thai females 45 79.711 7.14 64.29-93.55 T:75.6%4
A: 95.6%T:24.4%A: 4.4%
T:0%A: 0%
Thai males 104 83.511 7.13 64.71-110.71 T: 60.6%4
A:82.7%T:36.5%A:15.4%
T:2.9%A: 1.9%
Results
Table3. DescriptivestatisticsforJapaneseandThaiwithtraditional(T)andadjusted(A)PIdefinitions*.
*T:Platymeric(PI≤84.9),Eurymeric(85.0≤PI≤99.9),Stenomeric(PI≥100.0) (Wescott2005);A:Platymeric(PI≤88.9),Eurymeric(89.0≤PI≤103.9),Stenomeric(PI≥104.0)(TallmanandWinburn2015).1Japanese femalesdifferfromJapanesemales (p=0.038);Thaifemales differfromThaimales (p=0.004).2 Japanesefemaleswhodiedduringtheearly19th/20thcentury(n=35)differ(moreplatymeric)fromthosewhodiedduringthe1960s/1970s(n=35;p=0.001).
3 Japanesemaleswhodiedduringtheearly19th/20thcentury(n=134)differ(moreplatymeric)fromthosewhodiedduringthe1960s/1970s(n=83;p=0.001).
4TheJapaneseandThaifemalesandmalesarelessplatymericthanWescott’s (2005)NativeAmericanfemales(85%)andmales(79%)usingtraditionalPIthresholds.
Test A-P M-L
Intraobserver .989 .963
Interobserver .981 .957
Table1. Intraclass correlationcoefficientsfor45re-measuredChibafemora.
Test Sample Sum ofsquares df Mean
square F Sig.
Between groupsJapanese 623.170 7 89.024 1.716 .105Thai 538.511 6 89.752 1.698 .126
WithingroupsJapanese 14471.572 279 51.869Thai 7505.363 142 52.855
TotalJapanese 15094.743 286Thai 8043.874 148
Table4. ANOVA:AgeeffectsonPIfor8Japanesegroupsand7Thaigroups.
Test Meas. Sum ofsquares df Mean
square F Sig.
BetweengroupsFML 773.479 7 110.497 2.035 .055MHD 544.093 3 181.364 3.335 .021*
WithingroupsFML 6948.492 128 54.285MDH 7177.878 132 54.378
TotalFML 7721.971 135MDH 7721.971 135
Table5. ANOVA:FMLandMHDeffectsonPIfor136Japaneseindividuals.
JapaneseandThaiindividualsdisplayconsiderablevariabilityinsubtrochantericsizeandshape.SubtrochantericancestryassessmentmethodsderivedfromNativeAmericandataexhibitreduceddiscriminatorypowerwhenappliedtothesetwomodernAsiangroups,thereforeunderscoringtheimportancefortheongoingdevelopmentandtestingofpopulation-specificmethods.Assuch,theamendedsectioninglinesandPIthresholdsshouldbeusedoverthosederivedfromNativeAmericanswhenpresentedwithremainspotentiallyoriginatingfromEastorSoutheastAsia.
Intra- andinter- observervariationintroduces1.2-4.3%errortomeasurements.Additionally,sex,timeperiod,andMHDaffectPI,whileFMLandagedonot.Thissuggeststhatsubtrochantericformisnotentirelyundergeneticcontrol,butisalsoundertheinfluenceofintrapopulation variation,biomechanicalstresses,secularchange,and/orbodysize/proportions,potentiallycomplicatingitsuseinancestryassessment.Despitethesecomplications,thisstudydemonstratesthatpopulation-specificPIthresholdsandA-PandM-LsectioninglinesareusefulandappropriateindiscriminatingmodernJapaneseandThaiindividualsfromsomenon-Asiangroupswhencautiouslyapplied.
DiscussionandConclusions
*Bonferonni testshowssignificantdifference(.024)inmeanPIsbetweenMHD≤40mmandMHD47- 50mm.
Group N MeanPIPI AP andML
Correct Incorrect Correct Incorrect
Japanese males 77 81.72 68.8% 31.2% 80.5% 19.5%
Euro-Americanmales 77 91.36 58.4% 41.6% 62.3% 37.7%
Table2. Cross-validateddiscriminantfunctionclassificationratesforJapaneseandEuro-Americanmales.
AdamsBJ,ByrdJE.2002.Interobserver variationofselectedpostcranialskeletalmeasurements.JournalofForensicSciences47:1193-1202.
GilbertR,GillGW.1990.AmetrictechniqueforidentifyingAmericanIndianfemora.In:GillGW,RhineS,editors.Skeletalattributionofrace:methodsforforensicanthropology.MaxwellMuseumofAnthropologyAnthropologicalPapersNo.4.Albuquerque:UniversityofNewMexico.p.97-99.
GillGW,RhineS.AppendixA.AmetrictechniqueforidentifyingAmericanIndianfemora,byGilbertR,GillGW.In:GillGW,RhineS,editors.Skeletalattributionofrace:methodsforforensicanthropology.MaxwellMuseumofAnthropologyAnthropologicalPapersNo.4.Albuquerque:UniversityofNewMexico.p.99.
McIlvaine BK,Schepartz LA.2015.FemoralsubtrochantericshapeinAlbania:implicationsforuseinforensicapplications.HOMO-JournalofComparativeBiology66:79-89.
TallmanSD,WinburnAP.2015.ForensicapplicabilityoffemursubtrochantericshapetoancestryassessmentinThaiandWhiteAmericanmales.JournalofForensicSciences(July2015;inpress).
WescottDJ.2005.Populationvariationinfemursubtrochantericshape.JournalofForensicSciences50:286-293.
WescottDJ,Srikanta D.2008.Assessingancestryusingfemursubtrochantericshaperevisited:testingtheassumptionsoftheGilbertandGillmethod.HOMO-JournalofComparativeHumanBiology59:347-363.
*PortionsofthisresearchweresupportedbytheNationalScienceFoundation(grant#1414742),theJapaneseSocietyforthePromotionofScience,andtheJointPOW/MIAAccountingCommand’sCentralIdentificationLaboratory.
Acknowledgements:AllyshaP.Winburn,CarrieA.Brown,Dr.YoshiharuMatsuno,Dr.Yoshikatsu Negishi,Dr.Panya Tuamsuk,KathrynE.Kulhavy
Figure2. ScatterplotofJapanese,Thai,andEuro-AmericanA-PandM-Lmeasurementswithtraditional(T)GillandRhine(1990)andamended(A)TallmanandWinburn(2015)sectioninglines.
(T) (A)
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