Psychological factors and future performance of football players: A systematic review with meta-analysis

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University of Groningen

Psychological factors and future performance of football players

Ivarsson, Andreas; Kilhage-Persson, Amanda; Martindale, Russell ; Priestley, David; Huijgen,

Barbara; Adern, Clare; McCall, Alan

Published in:

Journal of Science and Medicine in Sport

DOI:

10.1016/j.jsams.2019.10.021

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2020

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Citation for published version (APA):

Ivarsson, A., Kilhage-Persson, A., Martindale, R., Priestley, D., Huijgen, B., Adern, C., & McCall, A. (2020).

Psychological factors and future performance of football players: A systematic review with meta-analysis.

Journal of Science and Medicine in Sport, 23(4), 415-420. https://doi.org/10.1016/j.jsams.2019.10.021

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ContentslistsavailableatScienceDirect

Journal

of

Science

and

Medicine

in

Sport

jo u rn al h om ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / j s a m s

Review

Psychological

factors

and

future

performance

of

football

players:

A

systematic

review

with

meta-analysis

Andreas

Ivarsson

a,c,g,∗

_,

_Amanda

_{Kilhage-Persson}

a

_,

_Russell

_Martindale

b,g

_,

David

Priestley

c,g

_,

_Barbara

_Huijgen

d,g,h

_,

_Clare

_Ardern

e,f

_,

_Alan

_McCall

b,c

a_Center_of_research_on_Welfare,_Health_and_Sport,_Halmstad_University,_Sweden b_School_of_Applied_Sciences,_Edinburgh_Napier_University,_UK

c_Arsenal_Performance_and_Research_Team,_Arsenal_Football_Club,_UK

d_Center_for_Human_Movement_Sciences,_University_Medical_Center_Groningen,_University_of_Groningen,_Netherlands e_Division_of_{Physiotherapy,}_Department_of_Medicine_&_Health,_Linköping_University,_Sweden

f_School_of_Allied_Health,_La_Trobe_University,_Australia

g_Arsenal_Psychology_and_Research_Group,_Arsenal_Football_Club,_UK h_Department_of_Psychology,_University_of_Groningen,_Netherlands

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received28May2019

Receivedinrevisedform4October2019 Accepted26October2019

Availableonline1November2019 Keywords:

Footballsuccess Performance Psychology

a

b

s

t

r

a

c

t

Objectives:Thissystematicreviewhad3keyobjectives:(1)toinvestigatewhetherpsychologicalfactors

wereassociatedwithfuturefootballperformance(e.g.,progressiontoprofessionalfootball,bettergame

statisticsduringthenextseason);(2)tocriticallyreviewthemethodologicalapproachesusedinthe

includedstudiesandsummarizetheevidenceforthecurrentresearchquestion;(3)toprovideguidelines

forfuturestudies.

Design:Systematicreview.

Methods:Electronicdatabases(SPORTDiscus,PubMedandPsycINFO)andpreviouslypublishedsystematic

andscopingreviewsweresearched.Onlyprospectivestudieswereconsideredforinclusion.

Results:Elevenpublishedstudiesthatreported39effectsizeswereincluded.Psychologicalfactors;

taskorientation,task-orientedcopingstrategiesandperceptual-cognitivefunctionshadsmalleffects

onfutureperformanceinfootball(ds=0.20–0.29).Duetohighriskofbiastherewerelowcertaintyof

evidenceforpsychologicalfactorsrelationshipwithfuturefootballperformance.

Conclusions:Psychologicalfactorsinvestigatedshowedsmalleffectsonfuturefootballperformance,

however,therewasoveralluncertaintyinthisevidenceduetovarioussourcesofbiasintheincluded

studies.Thereforepsychologicalfactorscannotbeusedasasoledecidingfactorinplayerrecruitment,

retention,releasestrategies,howeveritwouldappearappropriatetoincludetheseintheoverall

decision-makingprocess.Future,studieswithmoreappropriateandrobustresearchdesignsareurgentlyneeded

toprovidemorecertaintyaroundtheiractualrole.

1. Introduction

Onekey goalof appliedsportscienceresearchshouldbeto provide evidence-informed recommendations that practitioners andotherkey stakeholders(coaches,theboardetc.)canuseto improvetheirdecision-making andultimately positivelyimpact theirpractice.1 _To_help,_research_should_be_guided_by_real-world

issuesthatcomedirectlyfromtheﬁeld/keystakeholders.In con-temporary professional football, psychology is an area that is gainingmoreattentioninboththeappliedsettingoffootballteams

∗ Correspondingauthor.Tel.:+4635167448. E-mailaddress:Andreas.Ivarsson@hh.se(A.Ivarsson).

andtheresearchliterature.Morespeciﬁcally,onemainfocuswithin bothappliedaswellasresearchworkistoimplement interven-tionprogramsaimedtofacilitatethedevelopmentofpsychological skills.Aquestionregardingpsychologicalfactorswasposedinour dailypractice:canand/orshouldpsychologicalfactorsguidethe selectionorde-selectiondecisionofplayers(i.e.asapartofthe recruitmentstrategytorecruit,retainorreleaseaplayer)based onpsychologicalfactors?Inotherwords,arepsychologicalfactors associatedwithfuturefootballperformance?

In one systematic review there were 48 psychosocial fac-torssuggestedasimportantfordevelopingsuccessful(talented) footballers.2 _Psychosocial _factors _were _classiﬁed _as: _(a)

psy-chological factors (e.g., self-control, task orientation, adaptive perfectionism,intrinsicmotivation,resilience,anticipatoryskills,

https://doi.org/10.1016/j.jsams.2019.10.021

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416 A.Ivarsson,A.Kilhage-Persson,R.Martindaleetal./JournalofScienceandMedicineinSport23(2020)415–420

copingstrategies),(b)externalsocialfactors(e.g.,autonomy sup-portive coaching, parenting styles, coach-player relationships, effectivelearningenvironment,talentdevelopmentenvironments) and,(c)player-levelbehavioralindicators(e.g.,adaptivelifestyle choicesandvolitionalbehaviors,qualityoffootballspeciﬁc prac-ticeandplay,appropriateuseofcopingstrategies).2_One_limitation,

however,isthatamajorityoftheincludedstudieshaduseda cross-sectionalor retrospectivedesign. Tonot measuretheproposed predictorspriortotheoutcomeisalimitationwhenitcomesto discussingcausality.3

Inarecentlypublishedsystematicreview,thatincludedonly prospectivestudies,theﬁndings revealedthat decision-making, highleveloftheachievementmotiveshopeforsuccess,andfear offailurewerestronglyassociatedwithfuturefootballsuccess.4

Morespeciﬁcally,theresultshighlightedthatperceptual-cognitive functions,closelyrelatedtodecision-making,maybeimportantfor footballers.Thisisinlinewithotherresearchsuggestingthat supe-riorperceptual-cogntivefunctionsmaybeespeciallyimportantfor footballers5_by_enhancing_the_ability_to_respond_to_rapidly

chang-ingscenarios.6_This_suggestion_is_logical_given_football_is_played

inanunpredictableenvironmentwhereplayersconstantlyreceive information,havetoprocessitandthenmakeanappropriate deci-sion(e.g.passandtowhom,shootornotandwhereorkeepthe ball,wheretorunornottoruni.e.positionalplayetc).Visual atten-tionanddecision-makingmay,therefore,beimportant.6_Working

memory,inhibitorycontrol,cognitive/mentalﬂexibility, anticipa-tionandpatternrecognitionareexamplesofperceptual-cognitive functionsthathavebeensuggestedasusefulforfutureperformance andthedevelopmentofelitefootballplayers.6,7

Onelimitation,inbothGledhillandcolleguesaswellasMurr andcolleguessystematicreviewsisthelackofinformationabout theweightedaverageeffectsizeofpsychologicalfactorsinﬂeunce onfuturefootballperformance.ThesystematicreviewofGledhill etal.2_did_not_provide_any_effect_sizes_for_the_{psychological}_factors

thattheyidentiﬁed,thereforeitisdifﬁculttoassignanimportance forexampleinourquestionoftowhatextentweshouldusethese inthedecisiontorecruit,retainorreleaseaplayer.WhileMurr etal.4_did_provide_strength_of_association_through_reporting_effect

sizesforeachoftheincludedstudiesnooverallweightedaverage effectsizewasreported.Anadditionallimitationisalsothat nei-therofthestudiesincludedpotentialmoderators(e.g.,age)that mightinﬂuencethestrengthoftheassociationbetween psycho-logicalfactorsandfuturefootballperformance.Understandingthe strengthoflinksbetweenpsychologicalfactorsandfuture perfor-manceanddevelopingfootballplayerswouldbeusefultoinform decisionmakersduringtherecruitmentstrategy.

Thereforeweaimed:(1)toinvestigatewhetherpsychological factorsareassociatedwithfuturefootballperformanceasdeﬁned bytheresearchﬁeld(e.g.,progression.toprofessionalfootball, per-formanceduringnextseason);(2)tocriticallyreviewthemethods usedintheincludedstudiesandsummarizetheevidenceforthe currentresearchquestion;(3)toprovideguidanceforfuture stud-ies.

2. Methods

This systematic review was registered on the PROSPERO database (registration CRD42017069799). The structure and reportingofthissystematicreviewfollowedthePRISMA8

guide-lines.

Weincludedstudiesiftheymetthefollowingthreecriteria: (a)wereofprospectivedesign;(b)investigatedtherelationshipor predictivepowerbetweenpsychologicalfactorsandfuture pro-gressionorperformanceinfootball;and(c)presentedstatistical datanecessary forcalculation ofCohen’sd effectsizes. For the

studieswherethenecessarystatisticaldatawerenotpresented, we requested the datafrom the correspondingauthor. Studies includingmaleandfemaleeliteorsub-elitefootball/soccerplayers wereeligible.

Wedeﬁnedthefutureperformanceinfootballoutcome accord-ingtothefollowingcriteria:selectedtoaspeciﬁcteamorhigher playinglevel,receivingacontractextension,professionalcontract (orequivalent,includingbeingretainedinanelite-levelteam)or superiortechnical/tacticalperformanceingamessuchasstatistics (e.g.,goalsandassists)frommatch-analysesorsubjectiveratings ofcoaches,technical/academydirectorsinthefutureseason(s).

WesearchedtheSPORTDiscus,PubMedandPsycINFOelectronic databasesusingtwosetsofsearchterms.Wealsohand-searched publishedpeer-reviewedarticles5,9_and_reference_lists_of_included

studiestoidentifyanystudiesthatwerenotfoundintheinitial elec-tronicdatabasesearch.Databasesweresearchedfrominceptionto July14,2018usingacombinationofkeywords:

SetI:(((cognitivefunction*ORexecutivefunction*ORworking memoryORinhibitorycontrolORcognitiveflexibility)ANDelite soccerORelitefootball)ANDsuccessinfootballORsuccessin soc-cer)ORtalentidentificationinsoccerORtalentidentificationin football.

SetII:(((psychology ORresilience ORcoping ORanxietyOR mentalORconfidenceORskillORpersonalityORmotivationOR questionnaire)ANDelitesoccerORelitefootball)ANDsuccessin footballORsuccessinsoccer)ORtalentidentificationinsoccerOR talentidentificationinfootball.

Intheﬁrststep,tworeviewersindependentlyscreenedtitles andabstractsforallarticlesidentiﬁedinthesearchprocedure.All articleshighlightedbythereviewersaspotentiallyeligiblewhere thenassessedforeligibilitybythesametworeviewers, indepen-dently.Anydisagreementsaboutstudiesthatshouldbeincluded orexcludedwereresolvedbyconsensus,orbyathirdreviewerif consensuscouldnotbereached.

Datawereextractedandcheckedbytworeviewers, indepen-dently.Disagreementswere,inlinewiththerecommendationsin PRISMA8_guidelines,_resolved_by_consensus,_or_by_a_third_reviewer

ifconsensuscouldnotbereached.DatawereenteredintoanExcel spreadsheet(seeSupplementB).Theinformationextractedfrom eachstudywas(i)studydesign,(ii)participantcharacteristics (gen-der,age,playinglevel),(iii)thepsychologicalattribute/sstudied and(iv)typeofoutcomemeasure.

Inthenextstepthetwo reviewers,independently, classiﬁed thepsychologicalattributes,collectedwithineachoftheselected articles,into theoreticaldomains. This classiﬁcationresulted in four different theoreticaldomains: task orientation, ego orien-tation,task-orientedcoping strategies, andperceptual-cognitive functions.Eachofthesetheoreticaldomainsaredescribedbelow.

Achevementgoalorientationswereinvestigatedinseveral stud-ies.Theseorientationswere,basedonpreviousresearch,classiﬁed intotwotheoreticaldomains:taskandegoorientation.10

To classify coping strategies a number of different frame-works have been used. One of the most frequently used is basedonthreedimensions;task-oriented,emotion-oriented,and avoidance-oriented.11 _In _the_{classiﬁcation}_process₁₂ _factors_all

consideredtobetask-orientedstrategies wereclassiﬁedtoone domain; Task-oriented coping strategies. More speciﬁcally,the task-orientedcopingstrategies“referstoactionsthatareemployed inordertochangeormastersomeaspectsofasituationthatis perceivedasstressful”.12(p.2)

Allfactorsassociatedwithperceptualandcognitiveprocesses wereclassiﬁedintoonedomain;perceptual-cognitivefunctions. Based on the theoretical assumption that the effects between perceptual-cognitive functions and future football performance might bedifferent dependingif a generalor a football-speciﬁc test were used13 _we _also _coded _the _data _into _two _subgroups:

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perceptual-cognitivefunctionsmeasuredingeneraltests(i.e.,tests wheretheathlete’sresponseswererelatedtogeneralstandardized perceptual-cognitive tests) and perceptual-cognitive functions measuredinfootball-specifictests(i.e.,testswheretheathlete’s responseswererelatedtofootball-specificquestions,videoclips orphotos)wasperformed.Anotherclassificationwedidinrelation tothecognitivefunctionswasbasedonage.Morespecifically,the meanageofthestudyparticipantsforeachstudywasextracted bythereviewerandincludedintotheinformationsheet.The rea-sonforthiswasthatcognitivefunctionsarelikelytodevelopasa functionofage.14_Both_these_{classifications}_were_later_used_in_two

separatemoderatoranalyses.

Theclassiﬁcationsfromthereviewerswerethencompared. Dis-agreementswereresolvedbyconsensus.Aminimumoftwoeffect sizeswererequiredtoinclude thetheoreticaldomainin meta-analysis.15

TheRiskofBiasAssessmentToolforNon-randomizedstudies (RoBANS)wasusedtoassesstheriskofbiasinincludedstudies.16

TheRoBANSconsistsofsixdomainsforevaluation,eachjudgedas “highrisk”,“unclearrisk”,or“lowrisk”bytwoindependent asses-sors(AI;AKP).TheRoBANSguidelineswerefollowedinthe evalua-tionprocess.16_{Disagreements}_were_resolved_by_consensus_or

con-sultationwithathirdassessor(AM),ifrequired.Forthejudgement ofitem2(accountingforconfoundingvariables),weconsidered ageandtraininghoursasthemostrelevantconfoundingvariables. All analyses were conducted using Comprehensive Meta-Analysis.17_Cohen’s_d_{coefﬁcients}_were_used_as_effect_size_estimates.

Intheﬁrststepof theanalyses, thestatisticaldata(e.g.,means andstandarddeviations,Cohen’sdeffectsizes,oddsratios, sam-ple sizes) were entered into the software. Next, we computed Cohen’sdeffectsizesbasedontheaggregatedatafrom individ-ualstudies.Tocorrectfor samplingerrors,each effectsizewas weightedforsamplesize,thenweusedalltheweightedCohen’s deffectsizestocalculatetheaverageCohen’sdeffect size.We usedthesuggestedcut-offforCohen’sd(small=0.2–0.5, moder-ate=0.5–0.8,andlarge=above0.8)tointerpretthemagnitudeof theeffects.18_The_I2_statistic_was_used_to_assess_{heterogeneity.}19

Weusedthefollowingcut-offstoguidetheinterpretationoftheI2

statistic:25%(low),50%(moderate),and75%(high).19_We_also

cal-culatedthefail-safenumber(FSN).TheFSNindicatesthenumber ofadditionalstudies,reportingnull-results(e.g.,notstatistically significanteffects),thatwould beneededtochangeapotential statisticallysignificantfindingtonotstatisticallysignificant.20

We conducted one meta-analysis, investigating if different domains of psychologicalfactors predicted future performance and/or progression in elite football. In these analyses baseline scoresonthepsychologicalfactorswerecomparedbetweenthe playerswhodemonstratedasuccessfulprogressiontoelitelevel orbetterperformanceinthefuture,andthose whodidnot. All resultswerereportedusingmeanCohen’sdeffectsizeswith95% conﬁdenceintervals(CI).Weconsideredresultstobestatistically signiﬁcantwhenp<0.05.

WeusedtheGradingofRecommendationsAssessment, Devel-opmentand Evaluation(GRADE)21 _methodology_to_evaluate_the

certainty oftheevidence forourresearchquestion (GRADEpro, McMasterUniversity,2015).TheGRADEisaframeworktopresent summariesofevidenceforaspeciﬁcresearch(orclinical) ques-tion,andtomakeclinicalpracticerecommendations.22_One_author

judgedthestrengthofevidenceas:high,moderate,low,orvery lowbased onﬁvedomains:methodologicallimitationscreating riskofbiaswithinthestudy,inconsistencyofresults,indirectness ofevidence,imprecisionofresults,andpublicationbias.21_A

sec-ondauthorreviewedtheGRADEjudgements.Anoverallcertainty ofevidenceclassification, basedontheclassificationofthefive domains,wasthendecided.Thefullprocessis describedinthe GRADEHandbook.21

Records identified through database searching (n = 1150)

Additional records identified through other sources (n =12)

Records screened (n = 1162)

Full-text articles assessed for eligibility

(n =63)

Records excluded (n = 1099)

Studies fulfilling the inclusion criteria (n=11)

Full-text articles excluded (n = 52) Studies included in quantitative synthesis (meta-analyses) (n= 11)

Fig.1.Descriptionoftheselectionprocessforincludedstudies.

3. Results

Theliteraturesearchidentiﬁed1163records.Weexcluded1099 recordsaftertitleandabstractscreening.Thefulltextarticlesofthe remaining64studieswereassessedforeligibility.Elevenstudies mettheinclusioncriteriaandwereincludedforreview (Fig.1). Themostcommonreasonforexclusionwasduetocross-sectional design.

Examplesofdeﬁnitionsoffuturefootballperformanceranged fromnumbersofgoalsandassistsduringthenextseasonto pro-gression to professional football. In the studies, the timing of administrationofpsychologicalmeasuresandthemeasureof foot-ballsuccessrangedfromimmediately,toselection/nonselection afteraqualiﬁcationtournamenttoupto15yearsafterthe psycho-logicaldatawerecollected(seeSupplementB).

Intotal,3070maleand26femalefootballplayersparticipated intheselectedstudies(seeSupplementB).Sixstudiesmeasured perceptual-cognitive functions,and fivemeasuredtask orienta-tion, four measured ego orientation, and six measured coping strategies. Theperceptual-cognitivefunctionsassessed included anticipation,inhibitorycontrol,workingmemory,cognitive flex-ibility, creativity,and planning(for acomplete summaryof the cognitivefunctionsmeasuredinthestudiesseeSupplementB). Examplesofidentifiedtask-orientedcopingstrategiesweremental preparation, concentration/attention,goal commitment,seeking socialsupport,andhopeforsuccess. Asummaryofallincluded studies,includingtheirmeasuresisprovidedinSupplementB.The 11studiesreported40effectsizes.

Tenstudieswereathighriskofbiasinatleast1RoBANSdomain (formoreinformationseeSupplementA).Allstudieswereatlow riskofselectionbiasforselectionofparticipants(item1).Five stud-ieshadadequatestatisticaladjustmentforconfoundingvariables (item2).Eightstudieswereathighriskofperformancebias(item 3)duetoinadequatemeasurementsofexposure(i.e.,self-reported psychologicalvariables).Noneofthestudieswereathighriskof biasdue toinadequateblindingof outcomemeasures(item4): elevenstudieswereatlowriskofbias.Fourstudieswereathighrisk ofattritionbiasduetoincompleteoutcomedatawhilefour stud-iesdidnotreportordiscussmissingdata(item5).Infourstudies, statisticalanalyseswereperformedtoshowthatthemissingdata couldbeconsideredtobemissingatrandom,andwejudgedthese

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418 A.Ivarsson,A.Kilhage-Persson,R.Martindaleetal./JournalofScienceandMedicineinSport23(2020)415–420 Table1

Resultsofmeta-analysisandhomogeneitytestsfortherelationshipbetweenpsychologicalfactorsandfootballsuccess.

Variable k ES(d) 95%CI FSN I2_(%)

Ego 4 0.06 −0.03,0.14 0 0

Task 5 0.28 0.07,0.50 18 40

Task-orientedcopingstrategies 12 0.20 0.11,0.28 91 13

Perceptualandcognitivefunctions 18 0.27 0.19,0.36 216 14

Perceptualandcognitivefunctions(football-speciﬁctests) 9 0.26 0.12,0.40 25 0

Perceptualandcognitivefunctions(generaltests) 9 0.29 0.16,0.42 81 42

Note:k:numberofeffectsizes;ES(d):effectsizes;CI:conﬁdenceintervals;FSN:fail-safenumber;NA=notavailable.

Table2

SummaryoftheGRADEevaluation.

Researchquestion Factorsthatmaydecreasecertaintyofevidence TestaccuracyCoE

Riskofbias Indirectness Inconsistency Imprecision Otherconsiderations

1 Serious Serious Notserious Notserious None Low

2 Serious Serious Notserious Serious None Verylow

Note:CoE=certaintyofevidence;1=shouldtaskorientationbeusedtopredictfuturesuccessinfootball?;2=shouldegoorientationbeusedtopredictfuturesuccessin football?;3=shouldtask-orientedcopingstrategiesbeusedtopredictfuturesuccessinfootball?;4=shouldperceptualandcognitivefunctionsmeasuredinfootball-speciﬁc testsbeusedtopredictfuturesuccessinfootball?;5=shouldperceptualandcognitivefunctionsmeasuredingeneraltestsbeusedtopredictfuturesuccessinfootball?

asbeingatlowriskofattritionbias.Becausenoneofthestudies reportedapre-registeredstudyprotocoltheriskofreportingbias wasunclearforallstudies(item6).

Perceptual-cognitivefunctionshad asmall,positive effecton futurefootballperformance(Cohen’sd=0.27,95%CI=0.19,0.36). Playerswithbetterfuture performanceaccordingtoour deﬁni-tion(e.g.,contractatelitelevel,moregoalsscoredduringthenext seasons)hadsuperiorperceptual-cognitivefunction.

Thereweresmalldifferencesineffectestimatesbetweenthe results from the football-specific perceptual-cognitive (Cohen’s d=0.26, 95% CI=0.12, 0.40) tests and the general perceptual-cognitivetests(Cohen’sd=0.29, 95%CI=0.16,0.42).Therewere small,andpositive,effects betweenfootball-specific perceptual-cognitivetest performanceandfuturefootballperformance and generalperceptual-cognitive testsperformanceandfuture foot-ballperformance.Ameta-regressionwasperformedtotestifage (i.e.,meanageoftheparticipants)wasrelatedtothemagnitude oftheeffect.Theresultshowednostatisticallysignificant relation-shipbetweenageandthemagnitudeofeffectsize(ˇ=0.004,95% CI=_−0.007,0.014).

Therewasasmall,positiveeffectoftaskorientationonfuture footballperformance(Cohen’sd=0.28,95%CI=0.07,0.50).There wasasmall,positiveeffectoftask-orientedcopingstrategieson futurefootballperformance(Cohen’sd=0.2095%CI=0.11,0.28). Therewasatrivialeffectofegoorientationonfuturefootball per-formance(Cohen’sd=0.06,95%CI=−0.03,0.14).Forasummaryof resultsseeTable1.

UsingtheGRADErecommendations,therewasverylowtolow certaintyevidencefor theassociationbetweentaskorientation, egoorientation,task-oriented copingstrategies and perceptual-cognitivefactors,andfutureeliteornon-elitefootballperformance

(Table2).Therefore,thereiscurrentlyuncertaintyinthelevelof

evidenceforpsychologicalfactorsandfuturefootballperformance.

4. Discussion

Ourresultsshowedthatpsychologicalfactors,taskorientation, task-oriented coping strategies, and perceptual-cognitive func-tions(measuredwithgeneralandfootball-speciﬁctests)hadsmall effects onfuture football performance. However, differences in outcomemeasures,andinadequateconsiderationofconfounding variableswerecommonmethodologicalissuesofincludedstudies

whichmeantthatoverall,thereisuncertaintyaroundthelevelof scientiﬁcevidenceforthepreciserole/sizeofroleforpsychological factorsandfuturefootballperformance.

Toourknowledge thisis theﬁrstsystematic review of psy-chologicalfactorsandfuture footballperformancethatincludes a meta-analysis procedure for psychological factors and their associationwith future football performance. More speciﬁcally, advantagsofmeta-analysis,incomparisontosystematicreviews, are;thegenerationofpreciseestimatesofeffectsizes,increased powerincomparisontosinglestudies,andtheanalyzisofthe het-erogeneityacrossstudies.23_Also,_“well_conducted_{meta-analyses}

allowsforamoreobjectiveappraisalofevidence”.23(p.1371) _Our

resultslendsupportandhopefullyadvancethecurrentresearch lit-eraturefromthesystematicreviewsofGledhilletal.2_who_support

psychologicalfactorsbutdidnotprovideanyeffectsizesandMurr etal.4_who_also,_presenting_effect_sizes_from_included_studies,

sug-gestapotentialrole,thoughwithoutperformingameta-analysis. It isnot surprisingthat wefoundonlysmall associationsas therearelikelymultiplefactorsthatinteracttoinﬂuenceaplayers’ futureperformance(anddevelopment)infootball.24_A

combina-tionoftechnicalandtacticalskills,anthropometric,physiological aswellaspsychologicalcharacteristicsandskillsareallinvolvedin thedevelopmentoffootballplayers.24_Not_to_mention_the_inﬂuence

oftheenvironmenttheyinhabit.Althoughalowerlevelof scien-tiﬁcevidencecomparedtosysteamticreviews,previousnarrative reviews(level5expertopinion)havealsosuggestedthat psycho-logicalfactorssuchasadversity-relatedexperiencesareessential forsuccessatthehighestlevelofsport.25

Despite ourﬁndingsof smallassociations, itis importantto acknowledgethatbasedonGRADErecommendations,theoverall certaintyofthisevidenceiscurrentlyunclear,giventhesourcesof biasfoundintheincludedstudies(seeTable2).Importantly,this doesnotmeanthattheassociationsdonotexist,butwecannot becertainoftheirpreciseroleandassuch,cautionand considera-tionoftheuncertaintyshouldbetakenwhenusingthisinformation toguiderecommendationsonplayerrecruitment,releaseor reten-tionstrategies,asinthecaseofourstudyi.e.donotoveremphasise theircontributionandhighlighttheiruseincombinationwithother information.

Overall,wecannotanddonotexcludethepotential contribu-tionofpsychologicalfactorstotheoveralldevelopmentandsuccess offootballersandtheirperformance,24,26_but_urgently_need_high

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quality,lowriskofbiasstudiestoimproveourconﬁdenceinthe practicalsetting.

Weidentiﬁedthreeimportantmethodologicalconsiderationsof theincludedstudiesinparticular,whichmayhaveimportant impli-cationsforfutureresearch:(1)usingecologicallyvalidassessments, (2)choosinganappropriateoutcomemeasure,and(3)choosingan appropriatestudydesign.

Futureresearchmustuseecologically validassessments.The studiesincludedinourreviewmeasuredpsychological character-istics(i.e.,taskand ego orientation)and coping strategies with self-reportquestionnaires.Thereareinconsistenciesbetweenan individual’sreportingofhowtheythinktheywillreactorfeel,and thebehavioursinthereal-lifesituation.27_Given_that_behaviours_are

closelyrelatedtosportperformance28_the_{inconsistencies}_between

self-report and observed behaviours are a major limitation. A limitation many authors acknowledge in applied setting work. Therefore,werecommend futurestudiesincludeobservationof behaviours.29_Despite_the_small_effects_for_the_relationship_between

future footballperformance and perceptual-cognitive functions, measuredwithboth sportspeciﬁcand generaltests,theuseof ﬁeld-basedtestsmightprovideamoreaccurateideawheter psy-chologicalfactorsarerelevanttofutureperformancei.e.relevant tothepitch.

Differencesinthedeﬁnitionoffuturefootballperformanceas an outcome mayaffect theapplied valueof previous research. Includedstudiesinoursystematicreviewusedavarietyofoverly broad performance outcomes, suchas becoming a professional footballplayer,goalsandassistsperformedduringaseason,and selectiontoafootballacademyattheageof16.Evenifthedirection ofeffectsishomogenousfortherelationshipbetween perceptual-cognitive functions and future performance in the prospective studies,itisdifﬁculttodrawstrongconclusionsbecausethe out-comesvaryandtheirappropriatenessmaybequestionable(e.g. of thegoalsand assistsduring thenext2 seasons).One might alsoquestionwhethergoalsandassistsrepresentsuccessful foot-ballperformancewhenadefender’sprimaryroleistostopgoals, nottoscoregoalsorsetthemup.Unfortunately,thisalsomakes theappliedcontributionof theprospectivestudieslow.Among theincludedstudies,therewereindividualarticlesthatdiduse morepracticaloutcomeswhichareprobablymorerelevanttokey stakeholders.Forexample,progressiontoprofessionalfootball(i.e., becomingelitefootballplayers4–15yearsafterthepsychological factorsweremeasured).30,31

Prospective research is required to investigate relationships between psychological factors and football performance. We excluded27 articlesthat didnot meet this criterion, highlight-ingthenumberofstudiesperformedwithasub-optimaldesignto answerourreviewquestion.Methodologically-soundstudies(i.e. usingprospectivedesignsand football-relevanttests), involving researchersandpractitionersfromdifferentﬁelds,arewarrantedto understandthemultidimensionalaspectsthatmighthelpdevelop successfulplayers(e.g.,Sarmento etal.24_)._Due_to_the

multifac-torialandcomplexpatternofvariablesthatmightinﬂuencethe likelihoodoffutureperformanceinfootball,itisdifﬁculttouse unidimensionalfactorstopredictwhich playerswillsucceed in thefuture.32_Instead,_studies_can_contribute_evidence_to_implement

differenttests,strategiesorprogramsthatmaybeassociatedwith futurefootballperformanceandthereforemayincreasethechance offuturesuccess.

5. Limitations

Theoverall effect sizesfor the studiesmeasuring severalof theconstructswereonlybasedonasmallnumberofeffectsizes overall.Thismightinﬂuencetheaccuracyoftheresultsforthis

category offactors.Relyingonthedefinitionsof futurefootball performancelimitsourresultsbecauseitisdifficulttogeneralize thefindingstoanyspecificperformanceindicator.The heterogene-ity ofdefinitions mayreducethegeneralisabilityof theresults. Also,withinseveralofthetheoreticaldomains(i.e.,task-oriented copingskillsandperceptual-cognitivefunctions)severaldifferent variables were included. Even if we followed previous recom-mendationsin constructingthesedomainsit is consideredasa limitationbecausetheheterogeneityofincludedvariabesmight infleuncetheintepretationoftheresults.

6. Conclusion

Psychologicalfactors(taskorientation,copingstrategies/skills and perceptual-cognitive functions)had small effects onfuture footballperformance,howeverthespeciﬁclevelofthisevidence iscurrentlyuncertainduetobiasesincurrentstudies.Despitethe uncertainty,psychologicalfactorsneverthelessshouldcontinueto bediscussed,trainedandresearchedasoneofseveralaspectsthat mightberelevanttofuturefootballperformanceandideally along-sideotherfactors(e.g.technical,tactical,physical)insitu.Future researchisurgentlyneededtoprovidemorecertaintyandtherefore higherconﬁdencethan currentlyavailablefor providing recom-mendationstokeydecision-makersinpractice.

Acknowledgements

Nosourcesoffundingwereusedtoassistinthepreparationof thisarticle.

AppendixA. Supplementarydata

Supplementarymaterialrelatedtothisarticlecanbefound,in theonlineversion,atdoi:https://doi.org/10.1016/j.jsams.2019.10.

021.

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