How to Use the Likert Scale in Statistical Analysis Blogpost 20.30 Statistics Café

Introduction

ALikertscale(pronounced/ˈlɪkərt/,[1]also/ˈlaɪkərt/)isapsychometricscalecommonlyusedinquestionnaires,andisthemostwidelyusedscaleinsurveyresearch,suchthatthetermisoftenusedinterchangeablywithratingscaleeventhoughthetwoarenotsynonymous.WhenrespondingtoaLikertquestionnaireitem,respondentsspecifytheirlevelofagreementtoastatement.Thescaleisnamedafteritsinventor,psychologistRensisLikert.[2]

Theformatofatypicalfive-levelLikertitemis:1.Stronglydisagree2.Disagree3.Neitheragreenordisagree4.Agree5.StronglyagreeAnimportantdistinctionmustbemadebetweenaLikertscaleandaLikertitem.TheLikertscaleisthesumofresponsesonseveralLikertitems.BecauseLikertitemsareoftenaccompaniedbyavisualanalogscale(e.g.,ahorizontalline,onwhichasubjectindicateshisorherresponsebycirclingorcheckingtick-marks),theitemsaresometimescalledscalesthemselves.Thisisthesourceofmuchconfusion;itisbetter,therefore,toreservethetermLikertscaletoapplytothesummatedscale,andLikertitemtorefertoanindividualitem.ALikertitemissimplyastatementthattherespondentisaskedtoevaluateaccordingtoanykindofsubjectiveorobjectivecriteria;generallythelevelofagreementordisagreementismeasured.Oftenfiveorderedresponselevelsareused,althoughmanypsychometriciansadvocateusingsevenorninelevels;arecentempiricalstudy[3]foundthata5-or7-pointscalemayproduceslightlyhighermeanscoresrelativetothehighestpossibleattainablescore,comparedtothoseproducedfroma10-pointscale,andthisdifferencewasstatisticallysignificant.Intermsoftheotherdatacharacteristics,therewasverylittledifferenceamongthescaleformatsintermsofvariationaboutthemean,skewnessorkurtosis.Likertscalingisabipolarscalingmethod,measuringeitherpositiveornegativeresponsetoastatement.Sometimesafour-pointscaleisused;thisisaforcedchoicemethodsincethemiddleoptionof"Neitheragreenordisagree"isnotavailable.Likertscalesmaybesubjecttodistortionfromseveralcauses.Respondentsmayavoidusingextremeresponsecategories(centraltendencybias);agreewithstatementsaspresented(acquiescencebias);ortrytoportraythemselvesortheirorganizationinamorefavorablelight(socialdesirabilitybias).Designingascalewithbalancedkeying(anequalnumberofpositiveandnegativestatements)canobviatetheproblemofacquiescencebias,sinceacquiescenceonpositivelykeyeditemswillbalanceacquiescenceonnegativelykeyeditems,butcentraltendencyandsocialdesirabilityaresomewhatmoreproblematic.

ScoringandAnalysisAfterthequestionnaireiscompleted,eachitemmaybeanalyzedseparatelyorinsomecasesitemresponsesmaybesummedtocreateascoreforagroupofitems.Hence,Likertscalesareoftencalledsummativescales.Likertresponseitemsareoftenbelievedtorepresentanintervallevelofmeasurement.Butthiscanonlybethecaseiftheintervalsbetweenthescalepointscorrespondtoempiricalobservationsinametricsense.Infact,theremayalsoappearphenomenawhichevenquestiontheordinalscalelevel.Forexample,inasetofitemsA,B,CratedwithaLikertscalecircularrelationslikeA>B,B>CandC>Acanappear.Thisoutcomeviolatestheaxiomoftransitivityfortheordinalscale.WhetherindividualLikertitemscanbeconsideredasinterval-leveldata,orwhethertheyshouldbeconsideredmerelyordered-categoricaldataisthesubjectofdisagreement.Manyregardsuchitemsonlyasordinaldata,because,especiallywhenusingonlyfivelevels,onecannotassumethatrespondentsperceiveallpairsofadjacentlevelsasequidistant.Ontheotherhand,often(asintheexampleabove)thewordingofresponselevelsclearlyimpliesasymmetryofresponselevelsaboutamiddlecategory;attheveryleast,suchanitemwouldfallbetweenordinal-andinterval-levelmeasurement;totreatitasmerelyordinalwouldloseinformation.Further,iftheitemisaccompaniedbyavisualanalogscale,whereequalspacingofresponselevelsisclearlyindicated,theargumentfortreatingitasinterval-leveldataisevenstronger.Whentreatedasordinaldata,Likertresponsescanbecollatedintobarcharts,centraltendencysummarizedbythemedianorthemode(butsomewouldsaynotthemean),dispersionsummarizedbytherangeacrossquartiles(butsomewouldsaynotthestandarddeviation),oranalyzedusingnon-parametrictests,e.g.chi-squaretest,Mann–Whitneytest,Wilcoxonsigned-ranktest,orKruskal–Wallistest.[4]ParametricanalysisofordinaryaveragesofLikertscaledataisalsojustifiablebytheCentralLimitTheorem,althoughsomewoulddisagreethatordinaryaveragesshouldbeusedforLikertscaledata.ResponsestoseveralLikertquestionsmaybesummed,providingthatallquestionsusethesameLikertscaleandthatthescaleisadefendableapproximationtoanintervalscale,inwhichcasetheymaybetreatedasintervaldatameasuringalatentvariable.Ifthesummedresponsesfulfilltheseassumptions,parametricstatisticaltestssuchastheanalysisofvariancecanbeapplied.Thesecanbeappliedonlywhenmorethan5Likertquestionsaresummed.[citationneeded]DatafromLikertscalesaresometimesreducedtothenominallevelbycombiningallagreeanddisagreeresponsesintotwocategoriesof"accept"and"reject".Thechi-square,CochranQ,orMcNemartestarecommonstatisticalproceduresusedafterthistransformation.Consensusbasedassessment(CBA)canbeusedtocreateanobjectivestandardforLikertscalesindomainswherenogenerallyacceptedstandardorobjectivestandardexists.Consensusbasedassessment(CBA)canbeusedtorefineorevenvalidategenerallyacceptedstandards.

BottomLineInstructions1.Getyourdatareadyforanalysisbycodingtheresponses.Forexample,let'ssayyouhaveasurveythatasksrespondentswhethertheyagreeordisagreewithasetofpositionsinapoliticalparty'splatform.Eachpositionisonesurveyquestion,andthescaleusesthefollowingresponses:Stronglyagree,agree,neutral,disagree,stronglydisagree.Inthisexample,we'llcodetheresponsesaccordingly:Stronglydisagree=1,disagree=2,neutral=3,agree=4,stronglyagree=5.

2.Remembertodifferentiatebetweenordinalandintervaldata,asthetwotypesrequiredifferentanalyticalapproaches.Ifthedataareordinal,wecansaythatonescoreishigherthananother.Wecannotsayhowmuchhigher,aswecanwithintervaldata,whichtellyouthedistancebetweentwopoints.HereisthepitfallwiththeLikertscale:manyresearcherswilltreatitasanintervalscale.Thisassumesthatthedifferencesbetweeneachresponseareequalindistance.ThetruthisthattheLikertscaledoesnottellusthat.Inourexamplehere,itonlytellsusthatthepeoplewithhigher-numberedresponsesaremoreinagreementwiththeparty'spositionsthanthosewiththelower-numberedresponses.

3.BeginanalyzingyourLikertscaledatawithdescriptivestatistics.Althoughitmaybetempting,resisttheurgetotakethenumericresponsesandcomputeamean.Addingaresponseof"stronglyagree"(5)totworesponsesof"disagree"(2)wouldgiveusameanof4,butwhatisthesignificanceofthatnumber?Fortunately,thereareothermeasuresofcentraltendencywecanusebesidesthemean.WithLikertscaledata,thebestmeasuretouseisthemode,orthemostfrequentresponse.Thismakesthesurveyresultsmucheasierfortheanalyst(nottomentiontheaudienceforyourpresentationorreport)tointerpret.Youalsocandisplaythedistributionofresponses(percentagesthatagree,disagree,etc.)inagraphic,suchasabarchart,withonebarforeachresponsecategory.

4.Proceednexttoinferentialtechniques,whichtesthypothesesposedbyresearchers.Therearemanyapproachesavailable,andthebestonedependsonthenatureofyourstudyandthequestionsyouaretryingtoanswer.Apopularapproachistoanalyzeresponsesusinganalysisofvariancetechniques,suchastheMannWhitneyorKruskalWallistest.Supposeinourexamplewewantedtoanalyzeresponsestoquestionsonforeignpolicypositionswithethnicityastheindependentvariable.Let'ssayourdataincludesresponsesfromAnglo,African-American,andHispanicrespondents,sowecouldanalyzeresponsesamongthethreegroupsofrespondentsusingtheKruskalWallistestofvariance.

5.Simplifyyoursurveydatafurtherbycombiningthefourresponsecategories(e.g.,stronglyagree,agree,disagree,stronglydisagree)intotwonominalcategories,suchasagree/disagree,accept/reject,etc.).Thisoffersotheranalysispossibilities.Thechisquaretestisoneapproachforanalyzingthedatainthisway.

Readmore:HowtoUsetheLikertScaleinStatisticalAnalysis|eHow.comhttp://www.ehow.com/how_4855078_use-likert-scale-statistical-analysis.html#ixzz1LGrJsRUS

BloggerOpinionsPerBlogger,“There'sahugedebateongoinginthesocial/behavioralsciencesoverwhetherLikertscalesshouldbetreatedasordinalorinterval.Countmeasonewhothinksit'sOKtotreatthemasinterval.Iwouldanalyzethedatabothways-withchi-squareandwithANOVA,andseehowitturnsout-iftheoutcomesarethesame,you'reallset.Ifyougetsomethingdifferentwitheachmethod,thenyouhavesomethinginteresting.Overall,youcantreatthescalesasintervalandrunmethodsthatcomparemeans,suchasANOVA.Thescalesarecloseenoughtointervalsothatthesemethodsshouldn'tleadyouastray.Intermsofhowyouwouldusechi-square,youcouldsetupacomparisonbetweenthegroupsyouwanttocontrast,anddotheanalysisonthefrequencyofeachchoice,betweenthegroups(i.e.,didonegroupchoose"agree"moreoftenthananothergroup).Itwouldbeachi-squaretestofindependence.Thecontingencytablecouldbesetupwithgroupsasrows,andscaleitemsas8columns.Thecellsofthetablewouldcontaintheresponsefrequencies.Forchi-squarepost-hoc,useasimplecomparisonoftwoindependentproportionswithaztest.