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Wind Speed Perception and Risk
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Title: Wind Speed Perception and Risk
Series Title: Agdas D, Webster GD, Masters FJ (2012) Wind Speed Perception and Risk. PLoS ONE 7(11): e49944. doi:10.1371/journal.pone.0049944
Physical Description: Journal Article
Creator: Agdas, Duzgun
Webster, Gregory D.
Masters, Forrest J.
Publisher: PLoS One
Publication Date: November 30, 2011
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Abstract: Background: How accurately do people perceive extreme wind speeds and how does that perception affect the perceived risk? Prior research on human–wind interaction has focused on comfort levels in urban settings or knock-down thresholds. No systematic experimental research has attempted to assess people’s ability to estimate extreme wind speeds and perceptions of their associated risks. Method: We exposed 76 people to 10, 20, 30, 40, 50, and 60 mph (4.5, 8.9, 13.4, 17.9, 22.3, and 26.8 m/s) winds in randomized orders and asked them to estimate wind speed and the corresponding risk they felt. Results: Multilevel modeling showed that people were accurate at lower wind speeds but overestimated wind speeds at higher levels. Wind speed perceptions mediated the direct relationship between actual wind speeds and perceptions of risk (i.e., the greater the perceived wind speed, the greater the perceived risk). The number of tropical cyclones people had experienced moderated the strength of the actual–perceived wind speed relationship; consequently, mediation was stronger for people who had experienced fewer storms. Conclusion: These findings provide a clearer understanding of wind and risk perception, which can aid development of public policy solutions toward communicating the severity and risks associated with natural disasters.
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Funding: The authors thank the Federal Alliance for Safe Homes (FLASH; http://www.flash.org) for supporting the research. Publication of this article was funded in part by the University of Florida Open-Access Publishing Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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WindSpeedPerceptionandRisk DuzgunAgdas 1 ,GregoryD.Webster 2 ,ForrestJ.Masters 1 1 EngineeringSchoolofSustainableInfrastructure&Environment,CollegeofEngineering,UniversityofFlorida,Gainesville,Florida,UnitedSta tesofAmerica, 2 DepartmentofPsychology,CollegeofLiberalArtsandSciences,UniversityofFlorida,Gainesville,Florida,UnitedStatesofAmerica Abstract Background: Howaccuratelydopeopleperceiveextremewindspeedsandhowdoesthatperceptionaffecttheperceived risk?Priorresearchonhumanwindinteractionhasfocusedoncomfortlevelsinurbansettingsorknock-downthresholds. Nosystematicexperimentalresearchhasattemptedtoassesspeople'sabilitytoestimateextremewindspeedsand perceptionsoftheirassociatedrisks. Method: Weexposed76peopleto10,20,30,40,50,and60mph(4.5,8.9,13.4,17.9,22.3,and26.8m/s)windsin randomizedordersandaskedthemtoestimatewindspeedandthecorrespondingrisktheyfelt. Results: Multilevelmodelingshowedthatpeoplewereaccurateatlowerwindspeedsbutoverestimatedwindspeedsat higherlevels.Windspeedperceptionsmediatedthedirectrelationshipbetweenactualwindspeedsandperceptionsofrisk (i.e.,thegreatertheperceivedwindspeed,thegreatertheperceivedrisk).Thenumberoftropicalcyclonespeoplehad experiencedmoderatedthestrengthoftheactualperceivedwindspeedrelationship;consequently,mediationwas strongerforpeoplewhohadexperiencedfewerstorms. Conclusion: Thesefindingsprovideaclearerunderstandingofwindandriskperception,whichcanaiddevelopmentof publicpolicysolutionstowardcommunicatingtheseverityandrisksassociatedwithnaturaldisasters. Citation: AgdasD,WebsterGD,MastersFJ(2012)WindSpeedPerceptionandRisk.PLoSONE7(11):e49944.doi:10.1371/journal.pone.0049944 Editor: LuisM.Martinez,CSIC-UnivMiguelHernandez,Spain Received March28,2012; Accepted October19,2012; Published November30,2012 Copyright: 2012Agdasetal.Thisisanopen-accessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense,whichpermits unrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalauthorandsourcearecredited. Funding: TheauthorsthanktheFederalAllianceforSafeHomes(FLASH;http://www.flash.org)forsupportingtheresearch.Publicationofthisarticlewasfu nded inpartbytheUniversityofFloridaOpen-AccessPublishingFund.Thefundershadnoroleinstudydesign,datacollectionandanalysis,decisiontopu blish,or preparationofthemanuscript. CompetingInterests: Theauthorshavedeclaredthatnocompetinginterestsexist. *E-mail:gdwebs@gmail.com Introduction Windistheprimaryagentfortwoofthemostdestructive naturalhazardsonearthhurricanesandtornadoes.Storm preparation,evacuation,andhazardmitigationdependsignificantlyonriskperception[1,2],andeffectivepolicymakingand implementationnecessitatesunderstandinghumanperceptionof hazardsandassociatedrisks[3].Priorexperimentalresearchon windhumaninteractionhasfocusedonpedestriancomfort'in urbanareas[46]byestablishingwindspeedthresholdsthatmake dailytaskschallenging,uncomfortable,orcausepeopletofeel unsafe[7].Findingswerelargelybasedontwo-choicesemantic responses(e.g.,gentle-violent,calm-gale,pleasant-annoying[4,8]) orcharacterizationsofphysicalresponses(e.g.,lossofbalance, shiftsinfootsteptrajectories[9,10]).Surprisingly,however, empiricalresearchislackingon(a)people'saccuracyinperceiving windspeedwhiletheyareexperiencingitand(b)people's perceptionofpersonalriskinresponsetowind.Understanding people'sperceptualaccuracyofextremewindspeedsisimportant becausestormsoftencausemassivepowerandcommunication disruptionsthatleavepeoplewithoutofficialweatherwarningsor reports.Theeffectivenessofweatherwarningsinconveyingthe actualrisksassociatedwithextremewindeventsmaybe suboptimalevenifinformationregardingwindspeedseverityis madeavailable[3,11].Ourgoalinthepresentexperimentwasto addresstheseshortcomingsbyexposingpeopletovariouswind speedstogainabetterunderstandingofwindandrisk perceptionfactorsthatcouldbekeyindevelopingbetterpolicy andwarningsystemsforextremewind-relatedevents.Thismight includesupplementingextremewind-relatedwarningsbyframing theminfamiliarcontexts(e.g.,awindofthisspeedorgreateris enoughtoknockoveraperson''). Thispresentexperimentexaminedhumanperceptionof extremewindsandassociatedrisks.Becausepriorresearchin establishedperceptualdomains(e.g.,vision,audition,justnoticeabledifferencesinweightperception)hasshownhumanperceptiontobeanonlineartransformofphysicalstimuli(e.g.,Weber Fechnerlaw),wepredictedthatpeoplewouldoverestimatewind speedsathighervelocities,andthatriskperceptionswouldfollowa similaracceleratingtrajectory.Wealsoexpectedthatwindspeed perceptionwouldmediatetherelationshipbetweenactualwind velocityandperceptionsofrisk;overestimatesofwindspeedwould relatetomoreperceivedrisk.Onanexploratorybasis,wealso examinedtheextenttowhichindividualdifferencesinpriorstorm experiencemoderatedtheserelationships. Methods EthicsStatement EthicalstandardsoutlinedbytheAmericanPsychological Associationwerefollowedintheconductofthisresearch,which wasapprovedbytheUniversityofFloridaInstitutionalReview PLOSONE|www.plosone.org1November2012|Volume7|Issue11|e49944

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Board.Allparticipantsgavetheirsignedconsentpriortopartaking intheexperiment. ParticipantsandProcedure Seventy-sixcollege-agestudents(18women,58men)aged18to 40years( M =23.47, SD =4.68)participatedinthestudy. Participantswerefirstgivensurveysontheirpriorexperiences withandbeliefsaboutextremeweatherphenomenaand associateddecision-making.Next,participantsdonnedprotective gear(goggles,waders,andhoodedraincoats)andaharnessthat attachedtoahandrailsystemlocated8ftdownwindofthejet, whichtheywereallowedtohold.Participantswerethenexposed to10,20,30,40,50,and60mph(4.5,8.9,13.4,17.9,22.3,and 26.8m/s)windspeedsfor20-sintervalsinpredetermined randomizedorders(seeVideoS1).Inbetweeneachwindexposure event(whichlasted < 10s),participantscommunicatedtheir estimateofthewindspeedandtheirestimateofpersonalinjury riskonascaleof0( noperceivedrisk )to10( dangerous )toanobserver standingoutsidethewindfield.Thus,thetotalexperiment durationwas < 3minforeachparticipant.Thetestingconditions (windspeedintensities,totalexposuretime,gear)wereidenticalfor allparticipants;onlytheorderofwindspeedswasrandomizedto controlforpossibleordereffects.Participantsweregivenno informationonthewindspeedintensitiestopreventpossiblebias; however,theywereinformedofthewindspeedsafterthe experiment. WindApparatus Eight54-in(1.37-m)diametervaneaxialfansforcedairthrough a10-ft 6 10-ft(3.05-m 6 3.05-m)squarejettogeneratethewind fieldinthetestchamber(Figure1).Hydraulicpowertothefans wasindividuallycontrolledtoregulatetheangularvelocityofthe fanstoreachadesiredflow.AnRMYoungWindMonitorlocated inthetestchambermeasuredwindspeed,whichwasreadbythe equipmentoperator. DataAnalysis Becauserepeatedestimateswerenestedwithinparticipants,we analyzedthedatawithmultilevelmodeling(MLM[12,13])using HLM[14]andMplus[15].Usingmaximumlikelihoodestimation,MLMcanmodelwithin-andbetween-personeffects simultaneously.Within-person(orbetween-trial)varianceinwind orriskperceptionwasmodeledatlevel1,andbetween-person variancewasmodeledatlevel2asafunctionofbetween-person means(intercepts)and,insomemodels,individualdifferencesin numberoftropicalcyclonesexperienced(i.e.,thetropicalstorms withsustainedwinds $ 39mphor63km/h,hereafterreferredto inshorthandasstorms'').Forexample,inoneanalysiswe modeledwindspeedperceptionasafunctionofactualwindspeed (level1)andnumberofstormsexperienced(level2).Thelevel-1 modelwas: WindSpeedPerception ti ~ p 0 i z p 1 i ActualWindSpeed !" i z p 2 i ActualWindSpeed 2 !" i z e ti 1 wherePerception ti representsthewindspeedestimateforSpeed t byPerson i .Eachperson'sPerceptionscoresaremodeledas functionsoftheirmeanorintercept( p 0 i )andthelinear( p 1 i )and quadratic( p 2 i )effectsofactualwindspeed.Theerrorterm, e ti capturesthelevel-1residualvarianceforeachperson. InMLM,thelevel-1interceptsandslopesforeachpersonare modeledatlevel2asafunctionofindividualdifferencesinthe numberoftropicalcyclonesexperienced(grand-mean-centeredat 5.05storms): p 0 i ~ b 00 z b 01 Storms !" z r 0 i p 1 i ~ b 10 z b 11 Storms !" z r 1 i p 2 i ~ b 20 z b 21 Storms !" z r 2 i 2 Here, p 0 i againrepresentsthemean(intercept)foreachperson. The b 00 coefficientrepresentsthegrandmeanthebetweenpersonaverageofeachperson'saverageintensityscoreforthe averagenumberofstormsexperienced.Thecoefficients b 10 and b 20 representthebetween-personaverageofthewithin-person linearandquadraticeffects(respectively)ofactualwindspeedon windspeedperceptions.Thecoefficients b 01 b 11 ,and b 21 representtheextenttowhichthewithin-personinterceptsand linearandquadraticeffects(respectively)aremoderatedby individualdifferencesinthenumberoftropicalcyclonespeople haveexperienced.Theerrorterms r 0 i r 1 i ,and r 2 i capturethelevel2residualvariancefortheirrespectiveeffects. Inthemultilevelmoderatedmediationmodelsbelow,thisMLM frameworkisexpandedtoincludemediationatlevel1witha continuouslevel-2moderator(numberoftropicalcyclones experienced).Wefollowedproceduresoutlinedinpriorwork [1618]. Results DescriptiveStatistics Table1listsdescriptivestatisticsforperceivedwindspeedand riskbyactualintensity. WindSpeedPerceptionasaFunctionofActualWind Speed Boththelinear( b 10 =1.311, SE =0.054, t 75 =24.23,partial correlation[ r p ]=.94)andquadratic( b 20 =0.0061, SE =0.0016, t 75 =3.80, r p =.40)effectsofactualwindspeedsonpeople's perceptionsofwindspeedsweresignificantlypositiveforthe averageperson( p s .05;Figures2and3).Forthismodel,76%and 24%ofthevariancewasatthebetween-andwithin-personlevels, respectively.Theaveragepersonwasreasonablyaccurateand perceptionwasfairlylinearatslowerwindspeeds,butthe perceivedwindspeedsdepartedfrombothaccuracyandlinearity athigherwindspeeds. Simpleeffectstests[19]showedthattheaverageperceptiondid notdiffersignificantlyfromactualwindspeedsat10and20mph (4.5and8.9m/s);however,beginningat30mph(13.4m/s),the averagepersonprogressivelyoverestimatedtheactualwindspeeds (Table2,left;Figures2and3).Wealsotestedtheextenttowhich theaverageperceptionsfitordepartedfromaone-to-oneaccuracy slopeacrossthesixwindspeeds.Thesimpleslopebetween perceivedandactualwindspeedswascomputedforeachoneof thesixwindspeedlevels(i.e.,1060mph;4.526.8m/s).Thisis equivalenttoaskingwhetherthelinestangenttothecurveateach oneofthesixspeedsissignificantlydifferentthantheone-to-one line(Figure4).At10mph(4.5m/s),thesimpleslopewasnot significantlydifferentfromaone-to-onerelationship;however, startingat20mph(8.9m/s),thesimpleslopesweresignificantly morepositivethantheone-to-onerelationship,suggestingthat peoplebecamelessaccurateaboutthewindfunction(departed fromlinearity)aswindspeedsincreased(Table2,right),whichis tobeexpectedasthewindforcesexertedonthehumanbodyare proportionaltothewindspeedsquared. WindSpeedPerceptionandRisk PLOSONE|www.plosone.org2November2012|Volume7|Issue11|e49944

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RiskasaFunctionofActualWindSpeed Boththelinear( b 10 =0.1336, SE =0.0045, t 75 =30.01, r p =.96) andquadratic( b 20 =0.00043, SE =0.00020, t 75 =2.14, r p =.24) effectsofwindspeedonpeople'sperceptionsofriskwereboth significantlypositivefortheaverageperson( p s .05;Figure5).A slopeof0.1336inModel1indicatesthat,forevery10-mph(4.5m/s)increaseinwindspeed,theaverageparticipant'sperception ofriskincrease1.336unitsona010scale.Forthismodel,67% and33%ofthevariancewasatthebetween-andwithin-person levels,respectively.Theaverageperson'sriskfunctionforactual windspeedswascurvilinearandconcaveup(accelerating; Figure5).Thistrendwassupportedviaaseriesofsimpleeffects testsateachwindspeed;forexample,thesimpleslopesat10and 60mph(4.5and26.8m/s)were0.112( SE =0.011, t 75 =9.80, r p =.75)and0.155( SE =0.011, t 75 =14.66, r p =.86),respectively ( p s .05). RiskasaFunctionofWindPerception Perceptionsofwindandriskwerelinearlyrelated( b 10 =0.1031, SE =0.0035, t 75 =29.46, p .05, r p =.96);nosignificantquadratic effectwaspresent( r p = 2 .06;Figure6).Aslopeof0.1031indicates that,forevery10-mph(4.5-m/s)increaseinperceivedwindspeed, theaverageparticipant'sperceptionofriskincreasedabout1.031 unitsona010scale.Forthismodel,65%and35%ofthe Figure1.Designandphotographsofthewindsimulator. Theupperleftpanelshowsthewindsimulator'sdesign;theotherthreepanels showphotographsofitfromdifferentangles. doi:10.1371/journal.pone.0049944.g001 Table1. Descriptivestatisticsforwindandriskperceptionsbyactualwindspeed. PerceivedWindSpeed(mph)PerceivedRiskona1to10Scale ActualWindSpeedmph(m/s)Range Mdn Mean SD Skew. Exc. Kurt.Range Mdn Mean SD Skew.Exc.Kurt. r 10(4.5)16010.010.28.23.4218.05051.00.810.871.846.12.15 20(8.9)44020.020.69.30.51 2 0.28052.01.681.120.43 2 0.17.45* 30(13.4)107530.033.713.60.580.21073.03.211.54 2 0.03 2 0.23.48* 40(17.9)109045.045.217.50.43 2 0.31194.04.461.690.661.23.72* 50(22.3)1511557.560.419.40.550.303106.05.991.790.26 2 0.51.45* 60(26.8)3013075.075.825.40.22 2 0.502108.07.341.89 2 0.57 2 0.18.65* Note. Nesting not takenintoaccountforthistable;dataaveragedacrosspersonsratherthanexaminingdatawithinpersons.Skew.=Skewness.Exc.Kurt.=Excess Kurtosis. r =correlationbetweenwindperceptionsandriskperceptions. N s=76participants,454observations(2datapointsmissingduetoproceduralerror). p .05. doi:10.1371/journal.pone.0049944.t001 WindSpeedPerceptionandRisk PLOSONE|www.plosone.org3November2012|Volume7|Issue11|e49944

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variancewasatthebetween-andthewithin-personlevels, respectively. NumberofStormsExperiencedModeratestheActual PerceivedWindRelationship Wetestedtheextenttowhichindividualdifferencesinthe numberoftropicalcyclonespeoplehadexperienced( n =75; range:010-or-more; Mdn =5.0, M =5.0, SD =3.0)moderatedthe within-personactualperceivedwindspeedrelationships.The purposewastodeterminewhetherthenumberoftropicalstorms peoplehadexperiencedrelatestotheaverageactualperceived windspeedrelationship.Numberofstormsexperiencedsignificantlymoderatedthelinear( b 11 = 2 0.037, SE =0.015, t 73 = 2 2.48, p .05, r p = 2 .28)butnotthequadratic ( b 21 = 2 0.00078, SE =0.00049, t 73 = 2 1.57, p =.12, r p = 2 .18) effectofactualwindspeedonwindperceptions(Figure7).(Itis unlikelythatfourparticipantsexperienced10ormoretropical cyclonesbasedontheirageandhistoricdata.Thereported exposureinaccuraciesmightrelatetomisperceptionsaboutthe environmentalconditionsthatconstitutetropicalcyclones.Nevertheless,whenwere-ranthemodelwithoutthesefourparticipants,numberofstormsexperiencedstillmoderatedthelinear effectofactualwindspeedsonwindspeedperception, b 11 = 2 0.034, SE =0.016, t 69 = 2 2.01, p .05, r p = 2 .23). Wedecomposedthismodelbyconductingsimpleeffecttestsat theminimum(0)andmaximum(10)reportedvaluesfornumberof tropicalcyclonesexperienced.Forpeoplewhoexperiencedno storms,boththelinear( b 10 =1.50, SE =0.10, t 73 =14.70, r p =.86) andquadratic( b 20 =0.0101, SE =0.0029, t 73 =3.52, r p =.38) effectsofactualwindspeedsonperceivedwindspeedwere significant( p s .05);moreover,people'saveragelinearslopeswere significantlydifferentfromaone-to-onerelationship( b 10 =0.50, SE =0.10, t 73 =4.93, p .05, d =1.15;Figure7,thicklight-gray curve).Incontrast,forpeoplewhoexperiencedtenormore storms,therelationshipwasstrictlylinear( b 10 =1.130, SE =0.081, t 73 =14.00, p .05, r p =.85)thequadraticeffect( b 20 =0.0023, SE =0.0030, t 73 =0.78, p =.44, r p =.09)wasnon-significant; moreover,people'saveragelinearslopesdidnotdiffersignificantly fromaone-to-onerelationship( b 10 =0.130, SE =0.081, t 73 =1.61, p =.11, d =0.38;Figure7,thickblackcurve).Onanexploratory basis,wealsotestedthesimplemoderationeffectofnumberof stormsexperiencedonwindperceptionat60mph(26.8m/s).At 60mph(26.8m/s),numberofstormsexperiencedmarginally (i.e., p .06)moderatedpeople'sperceptionsofwindspeed ( b 01 = 2 1.65, SE =0.85, t 73 = 2 1.95, p =.055, r p = 2 .22; Figure7,rightmostendsofcurves). Figure2.Multilevelmodelingresultsforperceivedwindspeedasafunctionofactualwindspeed. Thingraylinesrepresentindividual predictedcurvesfor76participants.Thickblacklinerepresentstheaveragecurve.Thinblacklinerepresentsaone-to-onerelationship. doi:10.1371/journal.pone.0049944.g002 Figure3.Perceivedwindspeedasafunctionofactualwind speed. Pointestimatesand95%confidenceintervalsareshownforthe averageslopeforeachwindspeedtested. doi:10.1371/journal.pone.0049944.g003 WindSpeedPerceptionandRisk PLOSONE|www.plosone.org4November2012|Volume7|Issue11|e49944

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WindPerceptionMediatestheWindRiskRelationship andStrengthenswithInexperience Wetestedamultilevelmoderatedmediationmodel(mediation atthelowerlevel,moderationattheupperlevel[16,17])toassess (a)ifwindperceptionsmediatedthedirectrelationshipbetween actualwindandriskperceptionsand(b)ifindividualdifferencesin experiencewithtropicalcyclonesmoderatedthestrengthofthe mediation.Wetestedonlylineareffectsbecause(a)theywere substantiallystrongerthanthequadraticeffectsand(b)the quadraticeffectofactualwindspeedonriskwasnon-significant aftercontrollingforwindperceptions.Becausealldirecteffects remainedsignificant,allresultsshowedpartial(vs.complete) mediation.AsshowninFigure8a,whenassessedatthemean numberoftropicalcyclonesexperienced,thedirectrelationship betweenactualwindandriskwassignificantlyattenuatedafter controllingforwindperception;theindirecteffectviawind perceptionwassignificant.Thedirectandindirecteffects accountedfor38%and62%ofthetotaleffect,respectively. Wenexttestedthestrengthofthemediation(viasimpleeffects tests)forpeoplewhohadexperiencednostormsor10-or-more storms(Figures8band8c,respectively).Peoplewhohad experiencednostormshadanespeciallystrongactualperceived windrelationshipandshowedasignificantmediationpattern.The directandindirecteffectsaccountedfor36%and64%ofthetotal effect,respectively.Incontrast,peoplewhohadexperienced10or morestormshadaweakerbutmoreaccurate(theiraverage slopedidnotdiffersignificantlyfromaone-to-onerelationship) actualperceivedwindrelationshipandshowedanon-significant mediationpattern,becausethe95%CIfortheindirecteffect includedzero(Figure8c).Thedirectandindirecteffects accountedfor41%and59%ofthetotaleffect,respectively. Figure4.Perceivedwindspeedasafunctionofactualwindspeed:Simpleslopes. Examplesofsimpleslopestangenttotheaveragecurve (thicksolidline)at20(dottedline)and50(dashedline)mph(8.9and22.3m/s).Slopesareshowninreferencetoaone-to-onerelationship(thinsoli d line). doi:10.1371/journal.pone.0049944.g004 Table2. Simpleeffects:Windperceptionasafunctionofactualwindspeed. ActualWindSpeedmph(m/s) Intercept(differencefromactual)Slope(differencefromone-to-one) b 00 SEt 75 d b 10 SEt 75 d 10(4.5)0.2510.8800.280.080.0060.0710.080.02 20(8.9)0.9201.0900.840.220.1280.0522.48*0.66 30(13.4)2.7981.3852.02*0.540.2510.0485.19*1.37 40(17.9)5.9101.6933.49*0.920.3720.06355.85*1.55 50(22.3)10.2342.1304.80*1.270.4930.0885.59*1.48 60(26.8)15.7702.8395.55*1.470.6140.1165.28*1.40 Note.N s=76participants,454observations(2datapointsmissingduetoproceduralerror). p .05. doi:10.1371/journal.pone.0049944.t002 WindSpeedPerceptionandRisk PLOSONE|www.plosone.org5November2012|Volume7|Issue11|e49944

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Discussion Webeganbyaskinghowaccuratelypeopleperceiveextreme windspeedsandhowtheirestimatesaffecttheirperceptionsof personalrisk.Thesearekeyquestionsforboththepsychologyof humanperceptionandpublicpolicyinresponsetoextremewindrelatedweatherevents.Thestudyresultsindicatethatonaverage (a)peopleoverestimatehigherwindspeeds( $ 20mphor8.9m/s) Figure5.Multilevelmodelingresultsforperceivedriskasafunctionofactualwindspeed. Thingraylinesrepresentindividualpredicted curvesfor76participants.Thickblacklinerepresentstheaveragecurve. doi:10.1371/journal.pone.0049944.g005 Figure6.Multilevelmodelingresultsforperceivedriskasafunctionofperceivedwindspeed. Thingraylinesareindividualpredicted curvesfor76participants.Thickblacklinerepresentstheaveragecurve. doi:10.1371/journal.pone.0049944.g006 WindSpeedPerceptionandRisk PLOSONE|www.plosone.org6November2012|Volume7|Issue11|e49944

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butarereasonablyaccurateatjudginglowerwindspeeds,(b)the simplerelationshipbetweenwindspeedandperceivedrisk becomesincreasinglypositiveathigherwindspeeds,(c)wind perceptionmediatestherelationshipbetweenactualwindspeed andrisk,and(d)thismediationpatternisstrongeramongpeople withnopriorexperiencewithtropicalcyclonesandweakenswith exposuretoeachadditionalstorm. Thenewknowledgegeneratedbythisresearchisusefulnotonly becauseitexpandsourunderstandingofhowpeopleperceive windandwind-relatedriskonapsychologicallevel,butalso becauseithaspotentiallylife-savingpublicpolicyimplicationson howinformationiscommunicatedpriortoandduringextreme weatherevents(e.g.,tornadoes,hurricanes).Althoughtheaverage personoverestimateshigherwindspeeds(e.g.,theyperceive60mph[26.8-m/s]windstobe75mph[33.5m/s]),thisrelationship ismoderatedbyindividualdifferencesinstormexposure;with eachadditiontropicalcyclonepeopleexperienced,peoplemade moreaccuratewindspeedestimatesonaverage.Thissuggeststhat exposuretorealstormsmayhelpcalibratepeople'sperceptions regardinghigherwindspeeds.Withsomeexposure,peoplemaybe abletogaugewindspeedsmoreaccurately.Futureresearchshould strivetoexaminetheprocessesbywhichindividualdifferencesin perceptualandriskjudgmentsform.Nevertheless,ourresultsalso highlightadisconnectbetweenwindperceptionandreality, perhapsbecauseofpeople'slackofexposuretohigh-velocitywind speeds.Forexample,inFloridathemosthurricane-pronestate intheU.S.manycoastalresidentshailfromoutsidethestate [20]andthushavenopriorexperiencewithlandfalling hurricanes.Thefindingsindicatedthatpeoplewhohavenot experiencedsustainedtropicalstormorhurricane-forcewindsare morepronetooverestimatingwindspeed,whichmaynegatively affecttheirdecision-makingaboutpreparationandevacuation. Forexample,amajorcivilproblemwithgovernment-issued evacuationsisthephenomenonofshadowevacuation,''inwhich peoplewhodo not needtoevacuatechosetodosoanyway, therebyunnecessarilyexacerbatingtrafficjamsalongevacuation routes,andfillinglimitedspacesinsheltersandhotelrooms[21]. Furtherresearchisrequiredtovalidatethesefindings,notonly Figure7.Perceivedwindspeedasafunctionofactualwind speedandnumberofstormsexperienced. doi:10.1371/journal.pone.0049944.g007 Figure8.Multilevelmoderatedmediationmodelresults. PanelA showsamoderatedmediationmodelshowingthat(a)perceivedwind speed(mph)partiallybutsignificantlymediatedtherelationshipsbetweenactualwindspeed(mph)andperceivedrisk(linearrelationshipsonly) and (b)numberofstormsexperienced(grand-meancentered)moderatedtherelationshipbetweenactualandperceivedwindspeed. PanelsB and C showsimpleeffectstestsofthemediationmodelatzeroandten-or-morestormsexperiences,respectively.Valuesareunstandardizedregression coefficients[95%CIs].Thedirectrelationshipbetweenactualwindspeedandperceivedriskisshowninparentheses. doi:10.1371/journal.pone.0049944.g008 WindSpeedPerceptionandRisk PLOSONE|www.plosone.org7November2012|Volume7|Issue11|e49944

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withamorediversesample,butalsowithamorespecificmeasure ofriskthatcandistinguishbetweenprobabilityandseverity. Althoughadditionalresearchneedstobedonebeforewecan makeanystrongrecommendationsregardingpublicpolicy,the presentresearchmaysuggestthepossibilityforintroducingarisk metricorcontextualaidtocharacterizewindspeedsinstorm advisories,particularlygiventhatthedifferencebetweenperceived andactualwindspeedcanbeshowntobeinterpretedasa differenceofoneortwocategoriesontheSaffirSimpson HurricaneWindScaleafive-categoryclassificationsystemfor hurricaneintensitybasedonwindvelocity.Suchadualsystemis usedforhailadvisories,wheretheU.S.NationalWeatherService reportsbothhaildiameterinformation(infractionalinches)and thesizeofacommonobject(e.g.,dime-sized,''quarter-sized,'' softball-sized'').Perhapswindspeedscouldbeaccompaniedby relevantinformationsuchasthiswindspeedissufficienttoknock overtheaverageperson.''Nevertheless,wecautionthatthe presentresearchispreliminary,andadditionalresearchthat focusesonpublicpolicyapplicationswillneedtobeundertaken beforeanyrecommendationscanbemade.Wehopeournovel experimentalfindingsonwindperceptionwillinformnotonlythe psychologyofriskbutalsofutureresearchonthebroaderpolicy implicationsextremeweatherpreparationandresponse. SupportingInformation VideoS1 Thisvideoshowsparticipantsbeingexposed tovariouswindspeedinthewindsimulator(seeMethod sectionoftextfordetails). Inthisarticle,participantswere exposedtodrywinds;however,forbettervisualization,thisvideo showswind-drivenrain,whichwasappliedseparatelyfora companionstudy. (MOV) Acknowledgments Wethankthefollowingengineers,technicians,andgraduatestudentsfor theirhelpincarryingoutthisresearch:SevcanAgdas,Antonio Balderrama,ScottBolton,CoreyCook,KevinFrost,AlexEsposito, AmandaGesselman,JamesJesteadt,CarlosLopez,CarlosRodriguez,and JasonSmith.Preliminaryfindingsfromthisresearchwerepresentedatthe NationalHurricaneCenter,Miami,Florida(February2012),atthe NationalHurricaneConferenceinOrlando,Florida(March2012),the FloridaGovernor'sHurricaneConferenceinFt.Lauderdale,Florida(May 2012),andtheSocietyforJudgmentandDecisionMakinginMinneapolis, Minnesota(November2012). AuthorContributions Conceivedanddesignedtheexperiments:DAGDWFJM.Performedthe experiments:DA.Analyzedthedata:DAGDW.Contributedreagents/ materials/analysistools:DAGDWFJM.Wrotethepaper:DAGDWFJM. 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