ASSERT – The Autism Symptom SElf-ReporT for adolescents and adults: Bifactor analysis and validation in a large
adolescent population
Maj-Britt Posserud
a,b,e,*, Kyrre Breivik
b, Christopher Gillberg
c, Astri J. Lundervold
b,d,eaDepartmentofChildandAdolescentPsychiatry,HaukelandUniversityHospital,5021Bergen,Norway
bRegionalCentreforChildandYouthMentalHealthandChildWelfare,UniHealth,UniResearch,P.O.Box7800,5020Bergen,Norway
cGillbergNeuropsychiatryCentre,InstituteofNeuroscienceandPhysiology,UniversityofGothenburg,41119Go¨teborg,Sweden
dDepartmentofBiologicalandMedicalPsychology,UniversityofBergen,P.O.Box7800,Bergen,Norway
eK.G.JebsenCentreforResearchonNeuropsychiatricDisorders,UniversityofBergen,P.O.Box7800,Bergen,Norway
1. Introduction
Theconceptofautismhasevolvedfromthedescriptionofseverecasesofinfantileautismaffectingabout0.02%(Kanner, 1943),tothemoderndayautismspectrumdisorder(ASD)encompassinganestimated1%ofthepopulation(Bairdetal., 2006;Brughaetal.,2011;Posserud,Lundervold,Lie,&Gillberg,2010).Needlesstosay,the‘‘1%ASD’’isnotthesameas‘‘0.02%
infantileautism’’.ThemajoritywithASDfunctionsatnormalornexttonormallevelscognitively,and manyalsolead independentlivesinadultage.Thebroadeningoftheconceptandgrowingpublicawarenesshasledtoasituationwhere ARTICLE INFO
Articlehistory:
Received26July2013
Receivedinrevisedform17September2013 Accepted19September2013
Availableonline28October2013
Keywords:
Autism ASD
Autismsymptoms Screen
Adolescents Adults Factoranalysis ASSERT Self-report
ABSTRACT
Withaviewtodevelopingabriefscreeninginstrumentforautismsymptomsinageneral populationofadolescents,sevenitemsfromtheAspergersyndrome(andhigh-functioning autism)diagnosticinterviewwereadaptedforuseasself-reportinanonlinequestionnaire for youths aged 16–19 years (N=10,220). The selected items target lack of social understanding(4items)andrigidandrepetitivebehaviorandinterests(RRBI;3items).
Factoranalyseswereperformed,andthesevenitemswerealsovalidatedagainstself- reportedASDdiagnosis.Beststatisticalmodelfitwasfoundforabifactormodelwithone generalfactorandtwodomainspecificfactorstiedtosocialdifficultiesandRRBI.Boththe generalandthedomainspecificfactorswereassociatedwithself-reportedASDdiagnoses.
Thescale(referredtoastheAutismSymptomSElf-ReporTforAdolescentsandAdults– ASSERT)hadgoodscreeningpropertieswithareceiveroperatingcurve-areaunderthe curve(ROC-AUC)of0.87andadiagnosticoddsratio(DOR)of15.8.Applyingamodified scoringofthescalefurtherimprovedthescreeningpropertiesleadingtoaROC-AUCof 0.89andaDORof24.9.TheASSERTholdspromiseasabriefself-reportscreenforautism symptomsinadolescents,andfurtherstudiesshouldexploreitsusefulnessforadults.
ß2013TheAuthors.PublishedbyElsevierLtd.
* Correspondingauthorat:PBU,HaukelandUniversityHospital,5021Bergen,Norway.Tel.:+4797641843.
E-mailaddresses:[email protected](M.-B.Posserud),[email protected](K.Breivik),[email protected](C.Gillberg), [email protected](A.J.Lundervold).
ContentslistsavailableatScienceDirect
Research in Developmental Disabilities
0891-4222ß2013TheAuthors.PublishedbyElsevierLtd.
http://dx.doi.org/10.1016/j.ridd.2013.09.032
Open access under CC BY license.
Open access under CC BY license.
adults,whohavenotbeendiagnosedinchildhood,seekhelpfortheirproblemswith(Brughaetal.,2011)isolationand feelingsofinadequacy.AdultserviceshavenotyetdevelopedtomeettheneedsforadultswithASD,and fewsupport programsarein placethattargetthespecificneeds ofthoseindividuals(Howlin,Alcock,&Burkin,2005).Adultsmay thereforeaccessservicesthatareatlossaswhattodo,sometimesevenoutrightuncooperative,duetolackofknowledge,and adearthofadequatetoolsandinterventionsforthisgroup.Theresearchcommunityandpublicservicesneedtoadapttothe newrealityofarelativelylargegroupofpeoplewithASD,orautismsymptomsthatperhapsdonotquitesurpassthelevel requiredforadisorderdiagnosis,who,withjustabitofsupportandadequateunderstanding,mightfunctionwellwiththeir socialdisability,butwho,ifnotproperlyunderstood,mightsuffergreatly.
Giventhatautismhastraditionallybeenconceptualizedasachildhooddisorder,thereisalackofinstrumentstoscreen for,assessanddiagnoseautisminadults.Mostdiagnosticinterviewsareintendedforcompletion/interviewby/withaparent orsomeoneelsewithintimatefirst-handknowledgeaboutthepersonaffected,includinginformationabouthis/herfirst yearsoflife.GiventhatadultswithsuspectedASDmaynotevenhavealivingparent,itmaybeverydifficulttoassessthe socialskillsbeforetheageofthree(diagnosticrequirementintheDSM-IV,butlessstringentlydefinedundertheDSM-5) (Diagnosticandstatisticalmanualofmentaldisorders:DSM-IV,2011).Whenitcomestoself-ratinginstruments,theautism quotient(AQ)anditsshorterversion(AQ-Short)aretheimportantexceptionstothelackofsuchinstruments(Baron-Cohen, Wheelwright,Skinner,Martin,&Clubley,2001;Hoekstraetal.,2011;Woodbury-Smith,Robinson,Wheelwright,&Baron- Cohen,2005). AlthoughtheAQ existsfor adolescents,this version is tobefilled in/completedby parents ofaffected individuals(Baron-Cohen,Hoekstra,Knickmeyer,&Wheelwright,2006).Tothebestofourknowledge,therearenoASDself- reportinstrumentsforadolescents.Mostadolescents,atleastintheory,dohaveanadulttoanswerforthem,butthereare instanceswhereanadultmaynotbeavailable,asitistypicallydifficulttogetholdofandbeabletocooperatewithpatients andparentstogetherinthelaterteenageyearsandyoungadulthood(Sanci,Sawyer,Kang,Haller,&Patton,2005).Infact,the largemajorityofadolescentsreportthatthelackofconfidentialhealthservicesimpedesthemfromseekinghelpfortheir problems(Thralletal.,2000).
Thegoalofthepresentstudywasthereforetoformulateandevaluateasetofself-reportitemsthatwouldvalidlycapture thelackofsocialunderstandingandrigidandrepetitivebehaviorandinterests(RRBI)thatsignalASDinadolescentsand youngadults(andthroughoutthelife-span).ItemsfromtheAspergersyndrome(andhigh-functioningautism)diagnostic interview(ASDI)(Gillberg,Rastam,&Wentz,2001)wereadaptedforthispurpose.AlthoughtheASDIisaninvestigator-rated interview,itemshadalreadybeenadaptedforself-reportandcomparedtotheparentalASDIinapreviousstudyofyoung adultsmaleswithAspergersyndrome(AS),showinggoodagreementon theseitemsacrossparentand patientratings (Cederlund,Hagberg,&Gillberg,2010).Wefurtheradaptedsevenitemscoveringsocialimpairment(4items)andRRBI(3 items)tofitourNorwegianpopulation-basedadolescentsurveyusinganonlinequestionnaireandrenamedthescaleAutism SymptomSElf-ReporTforAdolescentsandAdults(ASSERT)toreflecttheintendeduseoftheseitems.Theaimsofthecurrent studywastoinvestigatethepsychometricpropertiesoftheASSERTanditsusabilityasascreeninginstrumentforthe presenceofautisticsymptoms.
PreviousstudieshavetendedtofindsupportforthefactthatASDconsistsoftwoormoredimensions/factorsthatareonly modestlycorrelatedwitheachother(Happe&Ronald,2008;Mandy&Skuse,2008;Shuster,Perry,Bebko,&Toplak,2013).
Thesefindingshavecontributedtothe‘‘fractionableautism’’hypothesiswhereproponentsarguethattheASDdimensions arelargelyindependentofeachotherwithlargelyseparatecauses.TherelationshipbetweenASD,socialdifficultiesandRRBI mustbesaidtobeunclear(Mandy&Skuse,2008),butinspiteofthis,thetwodomainshavenowbeeninseparablylinkedto ASDintheDSM-5,asadiagnosisofASDcannotbemadewithouthavingRRBIsymptoms(McPartland,Reichow,&Volkmar, 2012).ManyfactoranalyseshavebeenperformedonASDsymptoms,buttoourknowledge,abifactormodelhasnotbeen applied(Shusteretal.,2013).Apotentialadvantagewiththebifactormodeloverthecorrelatedfactormodel(wherethe dimensionsaretreatedascorrelatedbutseparate)isthatitprovidesinformationaboutwhatalloftheitemshaveincommon aswellasuniquesymptomdimensions.Ittherebyprovidesarationalstructureexplainingbothoverlapandseparability betweendimensionsinamodel,andcouldthusbeusefultoexplorethecontradictoryfindingsregardingASD,RRBIand sociability.Tothisaimandtoexaminethepsychometricpropertiesofthescale,weappliedbothaconventionalexploratory factoranalysis(EFA)andaconfirmatoryfactoranalysis(CFA)usingabifactormodel.Wewerealsointerestedinwhetherthe generalfactorpredictedself-reportedASDdiagnosisupandabovewhatwaspredictedfromtheuniquevariancetiedtothe subdomains(controlledforthegeneralfactor).
2. Materialandmethods 2.1. Populationsample
ThebackdropofthestudywasthefourthwaveofthelongitudinalBergenChildStudy(BCS).Inthiswave,theoriginal targetpopulationwasextendedtoincludeallyoungpeoplebornin1993–1995(age16–19yearsatthetimeofthestudy) residinginthecountyofHordalandwhereBergencityissituated(N=19121).Thiscross-sectionalstudyofalargergroupof adolescentswasnamed‘‘ung@hordaland’’(young@hordaland).Thecollectionofdatawasperformedinthespringof2012, and10,220youngpeopleparticipated(withacorrespondingresponserateof54%).Allyouthswereinvitedtoparticipate,but thegreatmajorityofresponsescamefromadolescentsattendingschools(97.8%),whereaschoollessonwassetasideto allowforthecompletionoftheonlinequestionnaire(bothprivateandpublicschools).
FurtherdetailsabouttheBCS/[email protected].
2.2. Instruments
Theung@hordalandquestionnairewasdevelopedspecificallyforthisstudywithaviewtocoveringawiderangeof mentalhealthproblemsandassociatedissues.Toscreenforautismsymptoms,sevenitemsfromtheAspergersyndrome (andhigh-functioningautism)diagnosticinterview(ASDI)(Gillbergetal.,2001)wereadaptedtogetherwiththemain developerofthatinstrument,ChristopherGillberg.TheASDIisasemi-structuredinvestigator-baseddiagnosticinterview including20items,andhasbeenusedinpreviousstudiesasavalidandreliabletooltodiagnoseAsperger/high-functioning autisminadults(Gillbergetal.,2001).Someoftheitemsareratedbytheinvestigatoraccordingtoobservedbehaviorduring theinterview.TheitemsfromtheASDIthatarenotinvestigator-ratedwereadaptedforanearlierstudyofyoungadultmales withAspergersyndrome(AS)inwhichtheywereusedasself-reportitemsandcomparedtoparentalreportsonthesame items(Cederlundetal.,2010).Theauthorsfoundthatmanywerequiteawareoftheirowndifficultiesinsomeareas,and arguedforincreasedconsiderationofthepatient’sownreportinthediagnosticwork-upandinterventionplanningfor patientswithASD.ThesamesevenitemsweretranslatedintoNorwegianandadaptedforuseintheonlineself-report questionnaireforadolescents16–19yearsofage.Fouritemstargetingsocialsymptoms(items1–4intheASDI)andthree itemstargetingrigidandrepetitivebehaviorandinterests(RRBI;items5,8and9intheASDI)wereincluded(Table1).
Responseoptionswere‘‘nottrue’’(score0)–‘‘somewhattrue’’(score1)–‘‘certainlytrue’’(score2),leadingtoascorerange of0–14p.ontheASSERT.
Theadolescentswerealsoaskedtoreportonthepresenceofpsychiatricdiagnoses:‘‘Haveyoubeendiagnosedwithany mentalhealthproblems?(e.g.ADHD,anxiety,depression,autism)’’.
2.3. Statisticalanalyses
ReportsmissingmorethanoneofthesevenASDIitemswerenotincludedintheanalyses(N=228).Receiveroperating curve(ROC)analyseswereperformedusingallsevenitemscombinedintoonescale(ASSERT)withself-reportedASDasstate variable.Descriptiveanalyses,Cronbach’salpha(
a
)andROCanalyseswereperformedusingIBMSPSSStatistics19.Mplus version 6.0 wasusedforother correlationanalysesandfactor analyses(Muthe´n &Muthe´n,1998–2012). The robust- weightedleastsquareestimator(WLSMV)wasusedinthefactoranalysesbecauseoftheskewedcategoricaldata(ordinal datawiththreeoptions).Usingpolychoriccorrelationsforestimation,theWLSMVseemsrelativelyrobusttoviolationsof normality(Dumenci&Achenbach,2008;Flora&Curran,2004).Thechi-squarevalueisnotreportedasmeasureofmodelfit asthisisnotexactwhenusingtheWLMSVestimator.Therefore,weusedBentler’scomparativefitindex(CFI;Bentler,1990), Tucker–Lewisindex(TLI;Tucker&Lewis,1973)andtheroot-mean-squareerrorofapproximation(RMSEA;Steiger&Lind, 1980)withcut-off values for CFI0.96, TLI0.95and RMSEA0.05 toindicate goodnessof fit (Yu,2002). EFA was performedwithgeominrotation(defaultobliquerotationinMplus).MissingdataononeASSERTitemwasreplacedwiththe meanoftheremainingsixitemsandincludedintheROCanalysesand correlationanalysesoftheentirescale. Inthe remaininganalyses,missingvaluesweretreatedwithpairwisedeletionfortheanalysesperformedinMplus(default)and withlistwisedeletionforanalysesperformedinSPSS(default).3. Results 3.1. Responses
Themeanscorefortheentirescalewas2.60(SD2.22,N=9992).DistributionofresponsesisshowninFig.1anditem responsefrequenciesinTable2.
MostindividualshadverylowscoresontheASSERT,and55%scored2points.Forty-fiveindividualsreportedhaving been diagnosed with an ASD (11 autism, 29 Asperger syndrome, 4 atypical autism/PDD-NOS, 1 possible autism), correspondingtoaprevalenceof0.45%self-reporteddiagnosedASD.
Table1
Thesevenself-reportitemsoftheAutismSymptomSElf-ReporT(ASSERT)adaptedfromtheAspergersyndromeandhighfunctioningautismdiagnostic interview(ASDI).
ItemabbreviationandtranslatedcontentoforiginalNorwegianitem
S1 Doyoufinditdifficulttosocializewith,ortogetintouchwithpeople,especiallypeopleyourownage?
S2 Doyouprefertobealoneratherthanbeingtogetherwithotherpeople?
S3 Doyouhavedifficultiesperceivingsocialcues?
S4 Dootherpeopletellyouthatyourbehaviororyouremotionalresponsesareinappropriateorhurtful?
R1 Doyouhaveastronginterestorhobbythatabsorbssomuchofyourtimethatithampersotheractivities?
R2 Doyouordootherpeoplefeelthatyouhaveverysetroutinesorthatyouareveryimmersedinyourowninterests?
R3 Doyouordootherpeoplefeelthatyouimposeyourroutinesorinterestsonothers?
3.2. Factoranalyses
Thethree-factorEFAsolutionshowedexcellentfit(CFI=1.00,TLI=1.00,RMSEA=0.00)forasolutionincludingaone- itemfactor(Table3).Thetwo-factormodelalmostmetpretestcriteria(CFI=0.98,TLI=0.94,RMSEA=0.06)andhadhigher itemloadings(Table2)whiletheone-factormodelwasdefinitelydiscarded(CFI=0.67,TLI=0.51andRMSEA=0.18).Table3 showstheitemloadingsforallthreeEFAfactormodels.Thecorrelationbetweenthefirst(social)andsecond(RRBI)factorin thetwo-factormodelwasr=0.23.
Thebifactormodelwithonegeneralfactorandtwosubdomains(socialandRRBI)showedverygoodstatisticalmodelfit withCFI=0.996,TLI=0.987andRMSEA=0.030.ThemodelwithitemloadingsisshowninFig.2.Evenifallitemloadings weresignificant(p<0.001,exceptS4loadingontothesocialsubdomain,withp=0.019),severaloftheloadingswererather weak(<0.50).Theitemsassessingdifficultysocializingwithpeople,stronginterestorhobbiesandhavingverysetroutines allhadloadingslowerthan0.40onthegeneralfactor.Thefactorswerecorrelatedwiththeself-reporteddiagnosisofASDto
0 200 400 600 800 1000 1200 1400 1600 1800 2000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
N
ASS ERT sc ore
Fig.1.DistributionofASSERTscoresinadolescents16–19yearsold(N=9992).
Table2
ResponsefrequenciesforeachASSERTiteminpercentagesandnumbers.
Item Nottrue Somewhattrue Certainlytrue
S1 70.6%(N=7051) 25.1%(N=2506) 4.4%(N=435)
S2 65.3%(N=6523) 28.9%(N=2885) 5.8%(N=581)
S3 82.7%(N=8262) 14.8%(N=1479) 2.5%(N=248)
S4 79.6%(N=7950) 18.5%(N=1844) 1.9%(N=192)
R1 48.3%(N=4824) 32.8%(N=3277) 18.9%(N=1887)
R2 54.0%(N=5394) 34.3%(N=3422) 11.7%(N=1172)
R3 85.7%(N=8560) 13.0%(N=1298) 1.3%(N=129)
Table3
Exploratoryfactoranalysis–itemloadingsfortheone-factor(F1),two-factor(F2)andthethreefactor(F3)solutions.Loadingsabove0.45arehigh-lighted (signaling20%overlappingvariance).
Item F1 F2 F3
Firstfactor Secondfactor Firstfactor Secondfactor Thirdfactor
S1 0.55 0.78 0.10 0.87 0.04 0.02
S2 0.52 0.63 0.04 0.55 0.08 0.11
S3 0.66 0.80 0.00 0.55 0.00 0.35
S4 0.46 0.48 0.12 0.00 0.01 0.78
R1 0.65 0.03 0.78 0.04 0.76 0.01
R2 0.70 0.01 0.85 0.01 0.88 0.02
R3 0.60 0.29 0.50 0.00 0.46 0.39
examinetheirrelevanceforadiagnosisofASD.Boththegeneralfactorandthesocialfactorhadmoderatecorrelationswith theASDdiagnosis(0.47and0.39respectively),indicatingthattheybothcontributeuniquelytopredictingthepresenceofan ASD,whiletheRRBIfactoronlycorrelated0.20withself-reporteddiagnosisofASD.
3.3. ASSERTscaleproperties
Cronbach’salpha(
a
)fortheentirescalewas0.62,probablyreflectingthemultidimensionalityofthescale.Cronbach’s alphawas0.63forboth thesocial subscale(ASSERTsoc)and therepetitiveand stereotypebehavior/interestssubscale (ASSERTrrbi),partlyanindicationoftheratherfewitemsincludedinthesubscales(4and3respectively).3.4. ValidityofASSERT
TheASSERTshowedgoodscreeningpropertiesversusself-reporteddiagnosisofASD,withanareaunderthecurve(AUC) intheROC-analysis(receiveroperatingcurve)of0.87(95%CI0.83–0.92)(Fig.3andTable4).Scoring5pointsontheASSERT hadasensitivityof0.80andspecificityof0.81forself-reportedASD.Nineadolescentswithself-reportedASDscored<5,but onlyoneoftheseadolescentsscoredexclusivelyontheASSERTrrbiitems,whereas33%oftheadolescentswithoutself- reporteddiagnosisofASDandascoreof2–4endorsedexclusivelyonthoseitems.Thecorrelationpatternbetweenthe factorsinthebifactorsolutionandself-reporteddiagnosisofASDindicatedthattheASSERTrrbiitemsareimportantmainly inconjunctionwiththesocialitems.Basedontheseresultswedecidedtoexploretheeffectofdifferentialweightingofthe itemsintheASSERT,bydoublingthescoreofthesocialitemswhilemaintainingthescoringoftheASSERTrrbiitems.This improvedthescreeningpropertiesfurtherleadingtoanAUCof0.89(95%CI0.84–0.93),sensitivityof0.80andspecificityof 0.86forascoreof8(Table4andFig.3).TheROCanalyseswerererunwiththeyouthswhohadresponded‘‘yes’’totheitem
‘‘Haveyoubeendiagnosedwithanymentalhealthproblems?(e.g.ADHD,anxiety,depression,autism)’’(N=724)toexamine thediscriminativepoweroftheASSERTforASDvs.othermentalhealthdisorders.AUCforthisgroupwas0.80(95%CI0.74–
0.86),andtheROCindicatedascoreof8(modifiedscoring)tobeoptimalalsointhisgroup.
3.5. ScreeningutilityofASSERT
TofurtherevaluatetheutilityofASSERTasdiagnostictestwecalculatedthediagnosticoddsratio(DOR).Thismeasureis moreinformativethanthepredictivevalueofatest,whichisinfluencedbythebaseprevalenceinthesampleinvestigated.
difficultsocialize
prefers being alone
perceiving social cues
inappropriate behav.
setroutines/immersed strong interest
imposing routines
Repetitive interests General
factor
Social difficulties
0.74
0.82
0.40 0.89
0.42
0.08 0.45 0.33
0.46
0.62
0.67
0.47 0.22
0.28
0.55
Self-reported ASD
0.39
0.20
Fig.2.Bifactormodelwithitemloadingsandcorrelationsbetweenfactorsandself-reportedASD.
TheDORisameasureofadiagnostictest’soverallaccuracy,andisgeneratedbydividingthenumberofcorrectlyclassifiedby thenumberofincorrectlyclassifiedindividuals(Glas,Lijmer,Prins,Bonsel,&Bossuyt,2003;Haynes,2006).Inotherwords,it tellsyouhowgoodthe‘‘sieve’’youareusingactuallyis.AnotheradvantageofreportingtheDORisthatitfacilitatesthe comparisonsoftestsformeta-analyses(Glasetal.,2003).ADORvalueof20ormoreindicatesthataninstrumenthasuseful screeningproperties(Fischer,Bachmann,&Jaeschke,2003).Usingthecut-offof5ontheASSERTproducesaDORof15.8, whileusingthecut-offof8onthemodifiedASSERTscoregivesaDORof24.9.Thisclearlyshowsthatalthoughthechange inspecificity ofusingthemodified ASSERTmayseem modest,it wasimprovedwithintact sensitivity,thereby much increasingthecorrectclassificationrateofthescale.
4. Discussion
ThepresentstudyshowedthatASSERTseemstoworkwellasaself-reportscreenforautisticsymptomsinthislarge population-basedsampleofadolescentsage16–19yearsold.Theitemsseemedtobereadilyunderstood,witharesponse rateof98.8%.Furthermore,theAUCfortheROCanalysisusingself-reporteddiagnosisofASDasoutcomewasashighas0.89, witha sensitivityof 0.80and aspecificity of0.86forscores8, supportingthevalidityof theASSERTas ascreening instrumentofASDsymptomsinadolescentsandyoungadults.Usingself-reportedASDdiagnosisforvalidationofASSERT wasnotideal,buttheoverallrateof0.45%ofself-reportedASDisalmostidenticaltooneofthepreviouslyreportedestimates fromtheBergenChildStudy(BCS)of0.44%basedontheDAWBA(developmentandwell-beingassessment)(Heiervangetal., 2007),andself-reportshaveprovenvalidforarangeofmentalhealthdisorders(Halmoyetal.,2010).Asthepresentfigureis basedonself-reportsfrommainlyhigh-schoolstudents,weassumethatthefigureof0.45%onlyincludeshigh-functioning individualswithanASD,andthattherateofadolescentswithanyASDshouldbehigher(Brughaetal.,2012).
Fig.3.ReceiveroperatingcurvesforASSERTandmodifiedASSERTversusself-reportedpresenceofASD(N=9992).
Table4
SensitivityandspecificityfortheASSERTscores.
ASSERT ModifiedASSERT
Score Sensitivity Specificity Sensitivity Specificity
1 1.00 0.19 1.00 0.19
2 1.00 0.37 1.00 0.29
3 0.92 0.55 1.00 0.45
4 0.88 0.69 0.91 0.55
5 0.80 0.81 0.87 0.67
6 0.65 0.89 0.87 0.75
7 0.47 0.94 0.82 0.82
8 0.35 0.97 0.80 0.86
9 0.26 0.99 0.60 0.90
10 0.22 0.99 0.58 0.93
11 0.14 1 0.47 0.95
12 0.10 1 0.38 0.97
13 0.08 1 0.33 0.98
14 0.00 1 0.29 0.99
15 – – 0.22 0.99
16 – – 0.20 0.99
17 – – 0.18 1.00
ASDsareconceptualizedintheDSM-5ascontainingtwocoregroupsofsymptoms,viz.socialimpairmentandRRBI.Many factoranalyseshavebeenperformedinthefieldofautism,bothinclinicalsamplesandlargerpopulation-basedsamples (Shusteretal.,2013),butnopreviousstudy(toourknowledge)hasappliedabifactormodel,inspiteofresearchindicating bothseparabilityofthedomainsinASD(geneticallyandinthepopulation)andunityofdomains(theASDs).Thebifactor modelhadgoodstatisticalfit,confirmingthatthesocialandRRBIdimensionsbothshareandhaveuniquevariancetiedto them.Despitethemodestcorrelation(r=0.23)betweenthetwosubdimensions(socialandRRBI)whenmodeledastwo correlatedfactors,thegeneralfactor(reflectingthesharedvariance)predictedself-reportedASDdiagnosis(r=0.47)over andabovewhatwaspredictedfromthetwodomainspecificfactors.ThisunderscorestheimportanceofnottreatingtheASD dimensionsastotallyseparatedimensionseveniftheyarenotstronglycorrelated.Atraditionalcorrelatedfactormodel wouldonlyhaveexploredhowwelleachofthetwosubdimensionswouldhavepredictedself-reportedASDdiagnosisby itselforcontrolledforeachother(theiruniqueprediction).Thisinformationisalsogivenbythebifactormodelshowingthat thedomainspecificsocialdifficultiesfactorhadastrongerassociationwithself-reportedASDdiagnosis(r=0.39)thanthe RRBIdomainspecificfactor(0.20).However,thebifactormodelfurtherindicatesthatthesharedvariancebetweenthetwo ASD subdimensions seemsto be equallyimportant as the unique contributionfrom social difficulties dimensionsin predictingself-reportedASDdiagnosis.
WearehesitanttoregardthegeneralfactorasrepresentingtheoverarchingASDconcept.Thebifactormodelhasoften beenappliedwhenrepresentingmultidimensionalconstructssuchasADHDandintelligencewhereitishypothesizedtobea dominant/overarching general factor in addition to some smaller domain specific factors (Ullebo, Breivik, Gillberg, Lundervold,&Posserud,2012). Thepresentstudygivessomesupporttothefractionable autismhypothesisas sucha dominantfactordoesnotseemtoexistregardingASDinthisgeneralpopulationsample.Ourgeneralfactorwasratherweak withlowloadingsofseveralitems,includingcoreASDsymptoms,suchashavingdifficultiessocializingwithotherpeople.
Thethreeitemswithstrongestloadingsontothegeneralfactorsuggestitcouldrepresenttheoryofmind(ToM)related difficulties more specifically(difficulties perceivingsocial cues (S3), and other peoples responsesto therespondents behavior(S4,R3)).Moreresearchisneededtobringconceptualclaritytowhatthegeneralfactorrepresentsandwhetherthe ratherweakloadingscouldbeduetoapplyingthemodelofanarrowdisordertoageneralpopulation.Themodelshouldbe replicatedinotherpopulationsandusingotherASDinstrumentsbeforeanystrongconclusionscanbedrawn.
AlthoughtherelationshipbetweenASD,socialdifficultiesandRRBIisunclearandinsufficientlyexplored(Mandy&Skuse, 2008),intheDSM-5,theASDdiagnosiscannotbemadeintheabsenceofRRBI(McPartlandetal.,2012).Simultaneously,a disorderofsocialcommunicationisintroduced.Thischangehasraisedcriticismandconcernamongresearchers,clinicians andparents,assomechildrenwithaclearsocialhandicapbutwithoutRRBIwillnolongerbelongwithintheASDcategory, withimplicationsforresearchandtreatment.SomestudieshaveshownthatanumberofchildrenwithASDaccordingtothe DSM-IVcriteria,donotmeetDSM-5criteriaforASD(Mayes,Black,&Tierney,2013).Someofthemwillmeetcriteriaforthe newsocialcommunicationdisorder.ItisuncertainwhatthedifferencebetweenASDandthenewsocialcommunication disorderis, apartfromnot includingRRBI(Skuse,2012; Tanguay, 2011). The correlationbetween theASSERTsocand ASSERTrrbiwaslow(r=0.23)butidenticaltootherpopulation-basedstudies(Ronald,Happe,&Plomin,2005;Ronaldetal., 2006),suggestingalowdegreeofoverlapbetweenthetwofactors.ThehighercorrelationwithanASDdiagnosisofthe generalfactorandthesocialfactormayindicatethattheoverlapbetweenthesocialandtheRRBIdomainsmayberather specifictoASDproblems.However,thespecificsocialfactorstillshowedamoderatecorrelation(r=0.39)withtheself- reportedASDdiagnosis,afteraccountingforthegeneralfactor.ThissuggeststhatanASDdiagnosismaybejustifiedalsoin theabsenceofclearRRBIsymptoms.Ifonebelongstothe‘‘splitter’’-advocateswithinthediagnosticsystem(ratherthan
‘‘lumpers’’)(McKusick,1969),onecouldalsoarguethatitsupportstheuseofaseparatedisorderincludingonlysocial difficulties,butthenatleastinthisstudytheyarenotdistinguishableatthesymptomlevel,otherthannotincludingRRBI symptoms.
TheDSM-5hasreplacedtheseparateASDswithonecategory.Inlinewiththisframeworkshift,theself-reportedautism diagnosesinthepresentstudywerecombinedanddichotomizedintopresenceorabsenceofASD.TheDSM-5furthermore indicatesthathavingASDanditsseverityissignaledbythepresenceanddegreeofimpairment.Thisintroducesacategorical elementwhichissituationalandnot(necessarily)directlyrelatedtotheunderlyingtrait.Similartootherlargepopulation- basedstudies(Constantinoetal.,2003;Posserud,Lundervold,&Gillberg,2006)thedistributionofautismsymptomsinthis sampleofadolescentsshowsagradualshiftfromnosymptomsuptohighsymptoms,supportingadimensionaldistribution.
However,thegoodfitofthebifactormodelincombinationwithaweakgeneralfactorcouldmeanthatthereareseparate populationswithinthepopulationfollowingdifferentdistributions.Thedimensionalmodelmaythusbeinsufficientin explaining the structure and nature of ASD symptoms, and models allowing for both categorical and dimensional distributionscouldbemoreadequate.
Althoughthetargetsampleinthisstudywas16–19yearsofage,thesameitemscouldmostlikelysuccessfullybeused acrosstheadultagespan,asindicatedbyapreviousstudyshowinggoodpropertiesofthesameitemsinyoungadults (Cederlundetal.,2010).Aself-reportinstrumentforASDvalidatedfromtheageof16isimportantasyouthsatthatagecan accesshealthservicesindependentlyanddenyparentscontactwiththesameservices.Althoughmostadolescentsdohavea livingparentwhocouldfilloutaquestionnaireforthem,itisnotalwayseasytoachieveasmanyadolescentsdonotdesire parentalinvolvement(Thralletal.,2000).
Morethan50%respondedpositivelytotheitem‘‘Doyouhaveastronginterestorhobbythatabsorbssomuchofyour timethatithampersotheractivities?’’indicatingpoordiscriminatorypropertiesforthisitemversusASD.Whenformulating
thisitemweconsideredotherwordingincluding‘‘narrow’’or‘‘circumscribed’’interesttoconveytheautisticnatureofthe interest.Whileitmighthaveimproveditsdiscriminatoryproperties,itmadetheitemdifficulttounderstand.Asautistic interestsarenotnecessarilycircumscribed,andtheborderlinebetweentheintensityofanautisticinterestandanintense normalinterestmaybehardtodefine,weoptedforreadabilityratherthanhighspecificity.Anintenseinterestintheabsence ofsocialdifficultiesisnottoberegardedasanautisticsymptom,andalowASSERTscorewhereallscoresstemfromR1toR3 canprobablybedisregarded.Thebifactormodelsolutionsupportsthis,asRRBIwhenincludedinthegeneralfactorwas relatedtoanASD,butafteraccountingforthegeneralfactoronlycorrelated0.20withreportedASD.Furthermore,modifying thescoringoftheASSERTbyweighingthesocialitemsmorethanRRBIitemsalsoimprovedspecificitywithintactsensitivity forASD.
4.1. Limitations
Thestudyreliedexclusivelyontheself-reported diagnosisofASD.Whilenot likelytoproducefalse positives,this procedureverylikelyproducesfalsenegativeanswers,e.g.fromindividualswhoindeedhaveanASDbutdonotreportitor whohavenotyetbeendiagnosed.Undiagnosedadolescentsmayalsobelessawareoftheirownproblems(thusscoringlow ontheASSERT).Thepresentprocedurecould,intheory,thereforebothunderestimateandinflatethepropertiesofthescale.
FuturestudiesshouldincludeclinicalassessmentofASDtoevaluatethescreeningpropertiesofASSERT.
Thefewitemsincludedmayhaveincreasedthelikelihoodofspuriousordistortedfindingsinthefactoranalyses.Thisalso appliestothescreeningpropertiesofthescale;moreitemscouldhaveincreasedthescreeningpropertiesandincreasedits usefulnessasaninformativemeasureofASDsymptomsaswell.However,brevitycanalsobeofmerit,especiallyregarding adolescentsandindividualswithcognitiveormentalhealthproblems,wherestayingfocusedonataskatlengthisoftena problem.However,furtherdevelopmentofthescaleincludingitemstargetingforinstancesocialcommunicationcouldbe advantageous.
Theprevalenceof0.45%forASDisprobablyanunderestimateonlyincludinghigherfunctioningindividualswithASD,but thisisalsothemostprevalentkindofASDandthegroupwhereself-reportprobablywouldbemostuseful.
5. Summary
Thepresentstudypresentsandvalidatestheuseofaself-reportscreenforautismsymptomsinadolescents–theAutism Symptom SElf-ReporT (ASSERT). The scale is briefand easily comprehended,and seemsto bevalid and useful with discriminationforthepresenceofanASDinboththegeneralpopulationofadolescentsandamongmoreclinicallyaffected adolescents.StudiesincludingclinicalassessmentareneededtodetermineitspotentialasascreenforASD.Abifactormodel ofthescalesupportedageneralfactorandtwoindependentfactorsofsocialdifficultiesandRRBI,butthegeneralfactorwas weak.ThemodelholdssomepromiseindescribingthestructureofASDtraitsinthegeneralpopulationbutitandother modelsshouldbeexploredfurther.
Acknowledgements
WethanktheBergenChildStudyresearchgroupthathasworkedtogetherformanyyears,andwhosejointefforthas madethestudypossible.AspecialthankstoKjellMortenStormarkandMariHysingintheBergenChildStudyleaderteam,to TormodBøeandHildeSackariassenfordatabaseworkandadministrativeeffort.Wearegratefulforthesupportofthe RegionalCentreforChildandYouthMentalHealthandChildWelfare,UniHealth,forhostingthestudyforalltheseyears.We alsothanktheHordalandCountyCouncilforcollaboratinginthestudyandallowingustoperformthestudyincollaboration withtheschools.WearegratefultoAnnaSpyrouforproof-readingthefinalmanuscript.Inparticular,wewouldliketothank alltheadolescents,parentsandteachersforparticipatinginstudy.
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