experimental-studyPPT课件

.,1,ExperimentalStudy,主讲：孙媛,.,2,1.Whatisanexperimentalmethod?,Experimentswerefirstusedinthenaturalsciences.Allofushavehadtheexperienceofundertakingeitheraphysicalorchemicalexperimentinalaboratory.Whathaveleftinyourmemorybytheseexperimentsaretubes,chemicals,wiresandothermaterials.Whatisanexperimentinasocialscience?Iwillanswerthisquestionfirstbyaconceptualdefinition.,.,3,2.Definition,Theexperimentalmethodisascientificmethodthatchangesgraduallyconditionsinplanunderacertaincontrol,andaccordingtoobservationrecordsandresearchdata,determinesthecausalitybetweenconditionsandthephenomenonbymeasuringtheaccompanyingphenomenaandchanges,thenfindsandsummariestheobjectivelawsofSecondLanguageAcquisition.,.,4,3.Thebasicpremiseofanexperiment,Thebasicpremiseofanexperimentisthatallfactorssaveoneareheldconstant.Thesinglefactorisvariedtoseewhateffectithasonthephenomenonunderinvestigation.Asstatedearlier,experimentshavetwocriteria:thereareatleasttwogroupsincludedinthestudy,acontrolgroupandanexperimentalgroup;thesubjectsarerandomlyassignedtooneofthosegroups.,.,5,5.Whydowehavetwogroups?,Thepurposeofhavingthetwogroupsinthestudyisthatifonegroupistreatedinonemanner,andanotherinadifferentmannerandtheirpost-treatmentbehaviordiffers,wecanconcludethatthebehaviordiffersasaconsequenceoftheirdifferenttreatments.Thiscanonlybeconcluded,ofcourse,ifthetwogroupsarecomparabletostartwith.,.,6,Randomgroupassignmentallowstheresearcherstoassumethattheyhavetwotrulycomparablegroupsattheoutsetoftheexperiment.Afurthersafeguardtoassuregroupcomparability(especiallydesirablewhensubjectpopulationsaresmall)istocomparetheirperformancesonapretest.Iftheexperimentalandcontrolgroupsareequivalentandonlythetreatmenttheyreceivediffers,thenanypost-treatmenttestdifferencescanbeattributedtothetreatmentitself.,.,7,6.Anexampleofanexperiment,HenrichsensfactorialdesignstudyingtheeffectofsandhivariationonthecomprehensibilityofEnglishinput.1.sandhivariation:itreferstophonologicalmodificationsuchascontraction,assimilation.2.thesubjectsoftheexperiment:nativeEnglish-speaker,ESLlearnerswithhighEnglishproficiencyandlowEnglishproficiency.3.Twotreatmentconditions:thepresenceorabsenceofsandhivariation.,.,8,1.Theadvantagesofanexperimentalmethodology,2.Thedisadvantagesandofanexperimentalmethodology,.,9,7.Summary,Experimentalstudiesareclassifiedaspre-experimental,quasi-experimentalandtrueexperimental,andcanbeplacedoncontinuumintermsofthedegreeoftheresearcherscontrol.Thepre-experimentalstudiesareleastcontrolledandthetrue-experimentalstudies,mostcontrolled.Thecriticalfeaturethatseparatesthesethreetypesofexperimentalstudiesistheextenttowhichcomparisongroupstolookalikeinallrespects.,.,10,Thebeststrategytomakethecomparisongroupssimilarisrandomassignmentofsubjects.True-experimentalstudiesarecharacterizedbyrandomizationwhilerandomizationisabsentintheothertwotypesofexperimentalstudies.Quasi-experimentalonesinvolvenaturallyoccurringtreatmentgroupsthatarefairlyclear-cut.Inthissense,althoughrandomizationisnotpresent,thedifferencesbetweenthetwogroupscanbeidentified,measuredandeventuallytheireffectscanbeextractedstatistically.Suchastatisticalcontrolmayenablethetreatmentconditionst