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DetectingandReducingSelectionBiasesinTalentIdentification

SingaporeNationalYouthSportsInstitute2017

DavidMannDepartmentofHumanMovementSciences

VrijeUniversiteitAmsterdamTheNetherlands

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THE BIRTHDATE EFFECTJUNIOR INTERNATIONAL FOOTBALLERS (U15-18)

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Helsen,vanWinckel &Williams,2005

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THE BIRTHDATE EFFECTJUNIOR INTERNATIONAL FOOTBALLERS (U15-18)

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THE BIRTHDATE EFFECTJUNIOR INTERNATIONAL FOOTBALLERS (U15-18)

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Whatisgoingonhere?

Whyisthe‘birthdateeffect’happening?

99 DepartmentofHumanMovementSciences

THE BIRTHDATE EFFECTCHANGE IN CUT-OFF DATE IN BELGIUM

Helsen,Starkes,&vanWinckel,2000 1010 DepartmentofHumanMovementSciences

THE BIRTHDATE EFFECTAUSTRALIAN CRICKETERS

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THE BIRTHDATE EFFECTALSO KNOWN AS “THE RELATIVE AGE EFFECT”

Achildbornatthestartofaselectionyear(usuallyJanuary)canbealmostafullyearolderthanachildbornattheendoftheselectionyear.

TheRelativeAgeEffectChildrenborntowardsthestartoftheselectionyeararerelatively

olderthanthosebornlaterintheselectionyear.

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THE BIRTHDATE EFFECTWHY DOES THE RELATIVE AGE EFFECT OCCUR?

• Beingrelativelyoldercanaffordalargeadvantageintermsof:- Height- Weight- Coordination- Strength- Cognitivedevelopment- Accumulationofpracticevolume

• Coachesmightthinkthattheyareselectingthemosttalentedplayersfortheirteams,buttheyareoftenjustpickingtheoldestchildren.- Theyareconfusingtalentwithage!- Theyareoftenchoosingteamstowinnow,ratherthanto

developthebestplayers.

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1313 DepartmentofHumanMovementSciences

THE BIRTHDATE EFFECTSUPER 14 RUGBY UNION PLAYERS

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Whyistheeffectstillpresentinadults?

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THE BIRTHDATE EFFECTWHY DOES THE EFFECT CONTINUE INTO ADULTHOOD?

Whyistherelativeageeffectstillpresenteveninadultteamswhenagecut-offsarenolongerrelevant?• Childrenidentifiedasbeing‘talented’get

accesstomoreopportunities:- Bettercoaching- Betterfacilities- Parentsaremorelikelytosupportandencourage

thechild- Thechildbelievestheyaregoodandaremorelikely

toinvestinpractice

• Childrenwhowerenotselected(generallythosebornlaterintheselectionyear)aremorelikelytodropout.

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THE BIRTHDATE EFFECTSTRONGER IN SOME SPORTS THAN OTHERS

Therelativeageeffecttendstobestrongerinsportswhere:1. Performancerelies(atleastinpart)on

sizeandstrength- e.g.,ice-hockey,Americanfootball,Basketball

2. Thereishighculturalimportance- e.g.,footballinEurope,ice-hockeyinCanada,

cricketinAustralia- Thereisalotofcompetitionforpositions,andso

thesmallestadvantagecounts!- Talentedathletestendtobeidentifiedatanearly

ageinthesesports,andrelativeagecountsmoretheyoungeryouare.

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THE RELATIVE AGE EFFECTWIDER SOCIETAL IMPACT

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RELATIVE AGE EFFECTTHEORIES

Wattie,Schorer,&Baker,2015;Sherar,Cumming,Eisenmann,Baxter-Jones&Malina,2010

Directeffects:performanceadvantagesasaresultofdifferencesinmaturation(size,strength,fitness,cognitivedevelopment)

Indirecteffects:evaluationsandreactionsofothers

Maturation-selectionhypothesis(e.g.,Cobley etal.,2009)

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RELATIVE AGE EFFECTHOW TO OVERCOME IT?

Options:i. Alterthebandwidthofjuniorage-groupsii. Birth-monthquotaswhenselectingteamsiii. Groupbyheightorweight(ratherthanage)iv. IncreasetheawarenessoftheRAE

(Barnsley,Thompson,&Legault,1992;Cobley etal.,2009;Helsen etal.,2012,1998;Musch&Grondin,2001)

AIMTodeterminewhethertheselectionbiasassociatedwiththeRAEcouldbereducedbyprovidinginformationabouttheage

oftheplayers

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THE BIRTHDATE EFFECTPSV JUNIORS

Barnsley,Thompson,&Barnsley,1985,J.CanadianAss.Health,P.E.&Recreation;Dudink,1994,Nature

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Percentageofplayersborninth

atquartile

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METHOD

Participants- 25maletalentscoutsfromPSV

FootballClub(Mage ± SD=56.0±10.8years)

- Toldtakingpartinastudyofbirthdateeffect

Task- Watchtwo4vs4small-sided

footballmatches(U-11s)- Scoutswereaskedtorankthe

players(1-8)accordingtotheirpotentialinthegame

Mann&vanGinneken,2017,JSS

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Department of Human Movement Sciences

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METHODTHREE GROUPS

No-agegroup Date-of-birth group Age-orderedshirtnumberinggroup

Listwithplayernames&nationality

Listwithplayernames&nationality

+date-of-birth ofeachplayer

Listwithplayernames&nationality

+date-of-birth ofeachplayer

+knowledgethatshirtnumbercorrespondedto

player’sage

Mann&vanGinneken,2017,JSS 2222 DepartmentofHumanMovementSciences

METHODDATA ANALYSIS

Selectionbias =correlationbetweenthescout’srankorderandtheshirtnumbers

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23518764

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12345678

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87654321

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46238715

r =+0.50 r =+1.0 r =-1.0 r =+0.02

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RESULTSSELECTION BIAS

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Sele

ctio

n bi

as No-age group

Date-of-birth group

Age-ordered shirt numbering group

*

*

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DISCUSSIONKEY FINDINGS

• Scoutshaveabiastoselectrelativelyolderplayers- Relativelyolderplayersbenefitfromindirecteffectofage

• ItispossibletoreducetheselectionbiasassociatedwithRA• Knowledgeoftheeffectandbirthdatesmaynotbeenough- ScoutsknewtheywereinastudyabouttheRAE!- Demonstratesthepervasivenessoftheeffect

• Amoresalientinterventionisrequiredtoreducetheselectionbias- Shirtnumberingpresentsinformation:

1. Inawaythatiseasytounderstand2. Inreal-time

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Let’slookatthebehaviour oftalentscoutsandcoaches

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WHAT ARE TALENT SCOUTS ACTUALLY ‘IDENTIFYING’?

• 15scoutsrankedU14femalehockeyplayersseenin4vs.4small-sidedgames

• Rankingswerecorrelatedwiththeplayers’scoresonarangeoftestsof:

i. Ageandmaturationii. Anthropometricsiii. Physiologicalcharacteristicsiv. Technicalskillv. Tacticalskill

Whataretheplayercharacteristicsthatmoststronglyinfluencetheselectionsoftalentscouts?

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WHO DO THE TALENT SCOUTS THINK THEY ARE SELECTING?

Scoutssaidthattheyprimarilylookforplayerswithgoodtechnical andtacticalskill

Scoutsreportthattheyprioritise %ofscouts1.Tactical skill 1002.Technicalskill(e.g.,dribbling) 793.Passingability 64

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WHAT ARE TALENT SCOUTS ACTUALLY ‘IDENTIFYING’?

-0.4

-0.2

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Correlationwith

scoutranking

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*

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WHAT ARE TALENT SCOUTS ACTUALLY ‘IDENTIFYING’?

-0.4

-0.2

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Partialcorrelatio

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scoutranking

(controllingforrelativeageandmaturation)

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Shorter

Heavier

Slower

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RELATIONSHIP BETWEEN PLAYER CHARACTERISTICS

Relativematuration

Relativeage

Height

Bodyweight

%Bod

yfat

BMI

Upp

erbod

ystrength

Endu

rance

Totalsprinttime

Peaksp

rinttime

Totaldrib

bletim

ePeakdrib

bletim

eAg

ility

Dribblingskill

Passingskill

Hittingskill

Tacticalsk

ill

Age-relatedparameters

RelativematurationRelativeage

Anthropometricparameters

HeightBodyweight%Bodyfat

BMI

Physiologicalparameters

UpperbodystrengthEndurance

TotalsprinttimePeaksprinttime

TotaldribbletimePeakdribbletime

Technicalandtacticalparameters

AgilityDribblingskillPassingskillHittingskillTacticalskill

+1.0

0

-1.0

Correlationbetweenparameters

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WHAT ARE TALENT SCOUTS ACTUALLY ‘IDENTIFYING’?

• Talentscoutssaidthattheywerescoutingfortacticalandtechnicalskill- Theirchoicesrevealedthatthesewerethefactorsleastrelatedtothe

selectionstheymade.• Scouts/coachesareinfluencedbyotherfactorsnotnecessarilyrelatedwith

long-termperformance.- Scoutsselectedchildrenlargelyonthebasisoftheirmaturation,rather

thanonparametersrelatedtotalent.- Theinfluenceofrelativematurationoutweighedthatofage.- Thesebiasesultimatelyledscoutstoselectplayerswhowereshorter,

heavier,andslower!

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ACKNOWLEDGEMENTS

Students/CollaboratorsPleun vanGinnekenEwout TimmermanAnoukSchmidtSophieVeermanSamCoenenJorran vanSanten

PSVFootballClubRini deGrootMaurovandeLooijRuudvanElkStanvanBijsterveldtBastiaan RiemersmaLucvanAgt

DavidMann

d.mann@vu.nl

@david_l_mann