Discovering Statistics: Experimental Project

Discovering Statistics: Experimental Project Overview Inthislaboratoryprojectyouwillhavetothinkupanexperiment,designtheexperimentyourselfandthencollectand analyseyourowndata.thisprojectisintendedtofitinwithwhatyou recurrentlystudyingonyourc8551cognitive PsychologymoduleandIhopethisenablesyoutodrawuponthisinformationtodevelopyourresearchideas. Inthefirstsessionyoushouldgetintosmallgroups(3K5people)anddiscusssomesimpleideasbasedontheideasin thishandout(whichareallaboutmemorybutyoudonothavetodoamemoryexperimentifyoudon twantto,as longastheexperimentaddressesatopiccoveredinc8551cognitivepsychology).youshoulddiscussyourideaswith yourseminartutor.usethenexttwoweekstorefineyourideasintoaninterestingresearchquestion,designyour experiment,andworkoutwhichstatisticalprocedureyouwillusetoanalyseyourdata.youshouldallowyourself4k5 weekstodesignthestudyandcollectdataandanother1k2weekstoanalysethedata.somethingstoremember: Think&about&how&you re&going&to&analyse&your&data&before&you&collect&it.thisisveryimportant,asitisa fundamentalprincipleofwellkconductedresearch.also,it sverysoulkdestroyingtocollectlotsofdataonlyto realisethattheycannotbeanalysed.yourseminartutors(andme)arehappytoofferadviceaboutanalysis beforeyoustartcollecting itismuchmoredifficultforusto salvage abadlydesignedexperiment. Don t&try&to&win&the&nobel&prize&for&science:thesearesmallscaleprojectssodon ttryanythingtoocomplex unlessyou reveryconfidentabouttheanalysisandexecution. Projectsinwhichyoudesignyourownstudygiveyouyourfirsttasteofdoingresearch(andactasa warmkup for your final year project). As such, it s very important that you embrace the opportunity to practice conducting research.don tworryifyoufinditdifficult itisaverytoughtransitionfromcarryingoutprojectstodesigningyour own.you might find the Field & Hole book (on your reading list) useful (Chapter 2 suggests how you can refine a researchquestion,andchapter3offerssomeadviceonexperimentaldesign). Collusion PleasenotetheUniversitiesregulationsonplagiarismandcollusiononline(linkedfromthestudydirectwebsite).The work on your laboratory report is a situation in which joint0 preparation0 is0 permitted0 by0 the0 examiners0 but0 joint0 production0is0not.tobeclear,your&submitted&work&must&be&unique&to&you.directsimilaritiesbetweenstudents reportswillbenoticedandwillbesubmittedtotheacademicmisconductofficerasacaseofcollusion.theoutcome ofthisprocessisunpleasantforeveryone,sopleasedon tdoit,anddon tlendotherpeopleyourwork. Because the studies on which the laboratory reports are based are designed collaboratively, in groups, we use commonsensetomakejudgementsaboutwhenreportsare toosimilar.however,fortheavoidanceofdoubt,thisis whatweexpect: Introduction:shouldbeprepared0and0produced0individually.Althoughyoumayendupreferringtosimilarsource materialtoothersinyourgroup,youareexpectedtoproducetheintroductionsectionentirelyonyourown.it shouldreflectyourownthinkingandyourownlogicalrationaleforthestudythatyourgroupdesigned. Method&section:will0be0prepared0jointly0in0the0sense0that0you0design0the0study0as0a0group,0but0must0be0produced0 individually.thatis,thewrittenmethodsectionmustbeuniquetoyou.wewilltakeintoaccountthatmethods sectionshaveastandardformatandthattherewillbeinherentsimilaritiesinthissectionformembersofthe same group; however, if similarities are so great as to indicate joint production/collusion the matter will be treatedasmisconduct. Results&section:you0are0permitted0to0analyse0the0data0collaboratively,0but0the0results0section0must0be0must0be0 produced0individually.thewrittenresultssectionmustbeuniquetoyou.thatis,evenifyouarereportingthe samestatistics/numericvaluesasothersinyourgroup,weexpectyourresultssectionstobepreparedcompletely independentlyandthatthiswillbereflectedinprosethatisuniquetoeachstudent. Discussion: must0 be0 prepared0 and0 produced0 individually. Although you may end up referring to similar source materialtopeopleinyourgroup,youareexpectedtoproducethediscussionsectionentirelyonyourown.it Prof.AndyField,2012 www.discoveringstatistics.com0 Page1

should reflect your own critical and theoretical analysis of the research study, your own thoughts on study limitationsandfutureresearch. Ethics Normallywhenwedoresearch,wehavetoensurethatourproceduresconformtoethicalcodesofconductandalso completeanethicsformthatisassessedbyauniversitypaneltoapprovetheprocedures.theproceduresforthis processattheuniversityofsussexcanbefoundhere:http://www.sussex.ac.uk/res/1k6k12.html Tosumup,theuniversityclassifiesresearchasbeingeitherhighorlowrisk.Fortheseprojects,thereisnotenough timetogothroughtheformalethicalprocedures,whichisoneofthereasonswhywegetyoutobaseyourworkon published research, which will have been subject to ethical clearance (in other words, the procedures should be ethical).instead,fortheseprojects,wehaveablanketethicalapprovalforanyprojectfallingwithintheremityou have(e.g.,acognitivepsychologyexperiment)thattheuniversitywoulddeem lowrisk,andforbidanyprojectthat wouldbeclassifiedas highrisk.someexamplesofprojectsthat&are&forbidden&because&they&would&be&high&riskare: Anyprojectinvolvinganyoneunder18yearsoldorothervulnerablegroups. Anyprojectinvolvingadministeringfoodordrugs(e.g.alcohol). Anyprojectthatinducespsychologicalstress,causeshumiliationor Anyprojectinvolvinghazardoussubstancesorequipment. Anyprojectinvolvingdeceptionofanykind. Inaddition,allprojectsonthismodulemust: Obtaininformedconsentfromeachparticipant(exampleconsentformsandinformationsheetscanbefound athttp://www.sussex.ac.uk/staff/research/spg/researchgovernance/apply) Anonymisealldataandtreatitconfidentially.Thisismosteasilydonebyassigningparticipantsanumeric codethatcannotbetracedbacktotheindividual. Beforerunningyourexperiment,youneedto: Read the BPS code of conduct for conducting research (http://www.bps.org.uk/theksociety/codekofk conduct/supportkforkresearchers_home.cfm). ReadtheSussexResearchGovernancewebsite:http://www.sussex.ac.uk/res/1K6K12.html Ifyourprojectis'lowrisk'thenyoumustbeabletorespond true tothesequestions: 1. Mystudydoesnotinvolveparticipantswhoareparticularlyvulnerableorunabletogiveinformed consent or in a dependent position (e.g. people under 18, people with learning difficulties, overk researchedgroupsorpeopleincarefacilities)? 2. Mystudywillnotrequireparticipantstotakepartwithouttheirconsentorknowledgeatthetime (e.g.,iwillnotusecovertobservationofpeopleinnonkpublicplaces),and/oriwillnotusedeception ofanykind. 3. Itwillnotbepossibletolinkidentitiesorinformationbacktoindividualparticipantsinanyway? 4. The study will not induce psychological stress or anxiety, produce humiliation or cause harm or consequencesbeyondtherisksencounteredintheeverydaylifeoftheparticipant. 5. No drugs, food, placebos, supplements, drinks or other substances will be administered and no invasiveorpotentiallyharmfulproceduresofanykindwillbeused. 6. The project will not involve working with any substances or equipment that may be considered hazardous. 7. No financial inducements (other than reasonable expenses, compensation for time or a lottery/drawticket)willbeofferedtoparticipants. Ifyoucouldanswertruetoall&of&the&abovequestionsandyoubelievethatyourexperimentaldesignfalls intothe lowrisk category,thenproceed. Ifyouansweredfalsetoanyofthesevenquestionsoryouthinkyourdesignfallsintothe highrisk categorythenyou must&not&do&it.instead,reviseyourideasuntilyourexperimentfallsintothelowriskcategory. Ifyouareinanydoubtaboutwhichcategoryyourprojectfallsintothenpleaseconsultwithyourpracticalclasstutor (who,ifinanydoubtwillconsultwithmeandthechairoftheethicscommittee). Prof.AndyField,2012 www.discoveringstatistics.com0 Page2

Ideas for Projects Introduction Memory is not a perfect representation of an experienced event as many notable commentators have stated. As BartlettstressesintheprefacetoRemembering, somewidelyheldviewshavetobecompletelydiscarded,andnone more completely than that which treats recall as the reexcitement in some way of fixed and changeless traces (Bartlett,1932,p.vi).Thefirstissueofthemostpopularintroductorypsychologytextbookclearlystates, manythings arerememberedthatneverhappenedatallorthatactuallyhappenedinwaysverydifferentfromthoserecalled (Hilgard,1953,p.270).Inhisseminaltextbook,Neisser(1967)callsthenotionthatmemorysimplyreactivates fixed orchangeless traces asthereappearance0hypothesis.hestatesthatitis soingrainedinourthinkingthatwerarely notice how poorly it fits experience (p. 282). Despite these claims, many psychologists still believed in the reappearance hypothesis. However, it was not until the midk1970 with a series of memory distortion studies by Loftus and colleagues (e.g., Loftus, Miller & Burns, 1978; Loftus & Palmer, 1974) that the malleability of human memorywasclearlydemonstrated. Howpeoplerememberaneventiscomplex.Informationfeedsintomemoryfrommanysources,notjusttheinitial perceptions,whichthemselvesarefilteredanddistortedastheypassthroughthecognitivesystem.whilethereare manydifferentmetaphorsortheoriesforhowmemoryworks(roediger,1980),thegeneralconsensusisthatmemory is reconstructive. An influential metaphor that Neisser (1967) used was of a paleontologist trying to construct a dinosaurfromafew storedfragments (i.e.,fossilizedbones)coupledwiththeoriesofpaleontology. 1 Memoriescan bereconstructedfromperhapsafewfragmentsofthefilteredperceptionsofourcognitivesystem,fromscriptbase knowledgeoftheeventtype,andfrominformationabouttheeventthatwasnotpartoftheinitialencoding.memory distortionscanarisefromanyofthesestages. Memorydistortionworkhasoftenbeenlinkedwithappliedconcerns.Inthe1980sthiswasdonemainlyinrelationto eyewitnesstestimonyandtoalesserextenttextprocessing.inthe1990stherecoveredmemorydebatedominated memoryresearch,withpsychologyandpsychiatrybeingpresented(ofteninabadlight)onthecoversofallthemain US news magazines, and with contradictory expert testimony producing multikmillion dollar legal settlements and imprisoninginnocentpeople(seeloftus,1997).further,therehasbeenalargeincreaseinchildrentestifyingincourt (Ceci & Bruck, 1993). The applied interests should not take away from the theoretical importance of memory distortionresearchtoourunderstandingofhumanmemory. There are several different procedures to examine memory distortion. The following is a partial list with a few thoughtsabouttheresearchapproachesandsomereferences.ihavenotlimitedthelisttooneswhereanovaktype designsareusuallyused,becauseyoumaydesignastudythatrequiresadifferentanalysisandthisisperfectlyok (youdonothavetouseanova). Agoodintroductiontomemorycanbefoundhere: http://www.exploratorium.edu/memory/index.html 1. Post-event information (PEI) ThisreferstotheclassicLoftusKlikestudieswherepeopleseeanevent,insomeform,thenaregivenapostKevent narrativewhich,forsomepeople,presentsmisleadinginformation,andthenparticipantsaretested.thisprocedure 1 NeissernotesthatHebbusedthismetaphorforfocalattention: Hebb s(1949,p.47)comparisonoftheperceiver with a palaeontologist, who carefully extracts a few fragments of what might be bones from a mass of irrelevant rubble and reconstructs the dinosaur that will eventually stand in the Museum of Natural History (1967, p. 94). Hebb s own description, a drawing or a report of what is seen tachistoscopically is not unlike a palaeontologist s reconstructionofearlymanfromatoothandarib, islessambitiousthanneisser selegantreconstruction.itisworth stating that Neisser still believes that memory is constructed, he just believes we no longer even have the few fossilizedremainstoaidthereconstruction,butthatmemoriesarecompleteconstructions. Prof.AndyField,2012 www.discoveringstatistics.com0 Page3

hasbeenusedmorethanotherproceduresandthereismuchresearchondifferencesincharacteristicsoftheevent, thepeiandtesting. Loftus,Miller&Burns(1978). McCloskey&Zaragoza(1985). 2. Deese-Roediger-McDermott Procedure InNorthAmerican,overthelasttenyears,itseemsthattoqualifyasamemoryresearcheryouhavetohaveusedthe DRMprocedure.Thisinvolvesshowingpeoplelistsofsemanticallyrelatedwords.Foreachlist,thereisacriticallure thatismissing.whenaskedtorecallthelists,peopleoftenincludethesecriticallures.listsareincludedattheendof theroedigerandmcdermott(1995)paper.theroedigerandmcdermott(1995)paperandsubsequentstudieshave usedwords.itwouldbenicetohavestudiesdesigned,whichusemoreecologicallyvalidstimuli(suchaspicturesor sounds).deese(1959)firstusedthistechnique,butthepaperwasnotwellknownwhenitfirstcameout. Roediger&McDermott(1995). 3. Biasing questions LoftusandPalmer(1974)showedpeopleseveralcarscrashesandthenaskedthemthevelocityofthecars.Theyused differentverbstodescribethespeed(forexample, hit and smashed )andfoundpeoplegavefasterestimatesthe higherimpliedspeedoftheverb.burtandpopple(1996)havemorerecentlyshownthisworksalsowithduration estimates.itisimportanttochooseacontinuousvariableastheresponsevariable. Loftus&Palmer(1974). Burt&Popple(1996). It might be worthwhile to look at the recent recommendations for avoiding biasing questions when interviewing eyewitness(http://www.ncjrs.gov/pdffiles1/nij/178240.pdf). 4. Memory implanting Therehavebeensomeimpressivestudies,withadultsandchildren,showingmemoriesforeventsthatdid0not0occur. Themostimpressivedemonstrationsaretherapistsgettingclientstobelievethattheywereabductedbyaliensor experienced biologically impossible events. The laboratory analogs involve getting people to remember some childhood events that happened (parents are usually contacted) and one that did not happen. This is probably impossibleforthecurrentassignment,becauseittakestimetocontactparents.still,someofyoumaycomeupwith goodideasonhowtodothiswithintheconstraintsoftheassignment. Loftus&Pickrell(1995). Hyman,Husband&Billings(1995). Garry&Gerrie(2005),CurrentDirectionsinPsychology(Reviewofthephotoshoptechnique) LoftushaswrittenapopularscienceintroductiontoCreatingFalsememories,whichcanbefound here: https://webfiles.uci.edu/eloftus/loftus_scientificamerican_good97.pdf?uniq=kjd60qg 5. Retrieval induced forgetting Anderson,BjorkandBjork(1994)showedparticipantsseveralsetsofwords.Thesetswere,forexample,alistoffruits. Later,participantswerereKpresentedwithhalftheitemsforhalfofthesets.Later,therewasarecalltest.Theitems thatwererepeatedwererecalledthebest.theitemsfromsetsnotpresentedwerethenextbestrecalled.theworst recalleditemswerethosefromthesetsfromwhichsomeitemswererecalled,butnotthose0particular0items.bjork andbjorkdescribehowtheretrievingofrelateditemsinhibitedmemoryfortheotheritemsintheset.thesesetsare includedinanappendixtoandersonetal.(1994). Prof.AndyField,2012 www.discoveringstatistics.com0 Page4

Anderson,Bjork&Bjork(1994). 6. Imagination inflation and dream interpretation Peoplearegivenalistofexperiencesandaskediftheyexperiencedthem.Theyarethenrequiredtoimaginesomeof these experiences. Later, they are asked the likelihood that the experienced really happened. Those experiences imaginedareratedasmorelikelythatthosenotimagined.inthemazzonietal.paper,theyusedreaminterpretation toincreaseeventlikelihood. Garry,Manning,Loftus&Sherman(1996). Mazzonietal.(1999). 7. Memory Conformity Ineyewitnesssituations,ifseveralpeopleseethesamecrimeandthendiscusstheeventthenoftentheirmemories will be different. When talking, what one person says can influence what the other person reports on later tests. SchneiderandWatkins(1996)showedthatthishappenedinamemorytestforwords.Wright,SelfandJustice(2000) showedthatthisworksalsowithmemoryofevents,andinfacttheeffectslookstrong. Schneider&Watkins(1996). Wright,Self&Justice(2000). Gabbert, F., Memon, A., & Wright, D. B. (2007). I saw it for longer than you: The relationship between perceived encoding duration and memory conformity. Acta0 Psychologica, 124, 319K331. (see: www2.fiu.edu/~dwright/research.htm) 8. You got em studies WellsandBradfield(1999)showedpeopleanevent,andthenhadthemtrytochoosetheculpritfromwhat sknown asa targetabsent,or blank,identificationparade(i.e.anidentificationparadeinwhichallsixofthepeoplewere nottheculprit).eventhoughthepeoplehadn tseentheculprit,iftheyweretoldthattheyhadchosenthecorrect personthennotonlywastheirestimatedconfidencehigher,butsowerecharacteristicslikehowlongtheysawthe culpritsface. Wright, D. B., & Skagerberg, E. M. (2007). PostKidentification feedback affects real eyewitnesses. Psychological0Science,18,172K178. o Available:www2.fiu.edu/~dwright/research.htm 9. Levels of Processing How well you remember something depends on how you processed it (how you thought about it), with deeper processing leading to better memory. Deep processing means attending to the meaning of the stimulus (its semantics ); shallow processing means attending to its physical attributes. (See, for example, Eysenck & Keane, Cognitive0Psychology:0A0student s0handbook,oranyothertextbookonmemory). HydeandJenkins(1973)showedparticipantsalistofwords.Howparticipantsprocessedthewordswasdetermined bywhichofthreeorientingtaskstheyweregiven: 1. Onegroupwereaskedtodetectan e ora g inthewords. 2. Onegrouphadtodecidethepartofspeechoftheword(e.g.noun,verb,etc). 3. Onegrouphadtoratethepleasantnessoftheword. Therationalewasthattoratethepleasantnessofawordyouhavetothinkaboutthemeaningofthatwordindepth. Therefore,peopleinthegroupwhomadetheseratingsshouldremembermore.Infact,theyfoundthatpleasantness ratingledtodoubletherecallcomparedtoonlylookingatphysicalattributes,likewhichlettersareintheword. Tominimizeparticipantstryingtoprocessthewordsinotherways,forhalftheparticipants,learningwasincidental (i.e.theywerenottoldtherewouldbeasubsequentmemorytest).fortheotherhalfoftheparticipants,learningwas intentional (they were told of the subsequent memory test). Hyde and Jenkins found no difference between Prof.AndyField,2012 www.discoveringstatistics.com0 Page5

participants who learnt intentionally and incidentally: The intention to remember in itself did not help people remember. 16 14 12 10 8 6 4 2 0 E-G checking Part of speech pleasantness rating Condition Foryourexperimentyoucouldlookatwhatsortoftasksmightimprovepeople smemorycomparedtoothertasks? YoucanremainclosetotheHydeandJenkinsexperiment,butitwouldbemoreinterestingtouseyourexperimentto provideananswertoaquestiontowhichyouwouldactuallyliketoknowtheanswer. How Similar Can My Experiment Be To Past Work? Youcan,ifyoulike,simplyreplicateoneofthestudiesthatIhavejustdescribed.However,bettermarkswillusually gotopeoplewhohavedonesomethingslightlydifferent.youcouldreplicateoneofthestudiesbutusingadifferent modality(say,replicateanexperimentusingvisualstimuli,butuseauditorystimuliinstead),oryoucouldimprovethe methodology(ifyoufeeltherewereproblemswiththeoriginalstudy).somepeopledocompletelynewthingsbutbe realistic:don tdesignsomethingwith58differentgroupsandthenspendeverywakinghourtryingtocollectthedata. Things to think about When Designing Your Experiment Data Analysis Youshouldusethemethodofanalysisthatismostappropriateforthedatathatyouhavecollected.Thismethod couldbeanythingthatyouhavebeentaughtinbothfirstandsecondyear.contrarytoapervasivemyth,youdonot have to analyze your data with an ANOVA. Unless, of course, an ANOVA is the most appropriate method for analyzingyourparticulardataset References Wehavejustputoneortworeferencesforeachsuggestedidea.Itwillbeworthsearchingformore.TheWebof Knowledge(http://wok.mimas.ac.uk/)willbeusefulforthis. Format of your Data Inmemoryresearchoftenthekeyresponsevariableiswhethersomebodyremembersanitem.Thisisnotappropriate forparametricstatisticaltestsbasedonthenormaldistribution(i.e.tktests,anovaetc.).acommonwaytoturnthis intoamorecontinuousvariableistoaskpeoplehowconfidenttheyareintheirmemories.pretendyouuseafivek pointscale,andthepersoneitherremembersordoesnotremember.youneedtocalculateanewvariable.ifthe personrememberstheevent,thenthenewvariableisequaltotheconfidencescore.ifthepersondoesnot,thenitis thenegativeoftheirconfidencescore. Remembers: Yes 1 2 3 4 5 No 1 2 3 4 5 NewVariable K1 K2 K3 K4 K5 0 1 2 3 4 5 Prof.AndyField,2012 www.discoveringstatistics.com0 Page6

Anotherusefulwayaroundthisistohaveseveraltargets(severalthingsthatyouwantpeopletoremember)anduse thenumber(orpercentage)thattheydorememberasyourdependentvariable. Youshouldstillcheckthedistributionalassumptions. Random assignment of participants to groups Participantsshouldberandomlyassignedtoyourexperimentalgroups(youcanaddtheconstraintthateachgroup hasanequalnumberofsubjects).thisisforacoupleofreasons. First, the way you run the experiment will subtly change as you run it. You may be more smooth or more or less motivatinginsubtleways.second,thesortofparticipantyoucanrecruitasyouruntheexperimentwillchangeasyou run the experiment. First you will ask your friends. Pretty soon you have used up your friends and you are on to acquaintances. By the 6 th participant you need to run complete strangers. Your friends may have certain common characteristics e.g.youallliketostudyhardoryouareallalcoholics.alsothefriendsyourunatfirstwillbetheones thatagreedquickly;thefriendsyourunlastwillbetheonesyouhadtotwistthearmoftogettodotheexperiment. Soifyoufinishgroup1firstthengroup2thenfinallygroup3,therecouldwellbeadifferenttypeofpersonineach group.iftherewasadifferencebetweenthegroups recallyouwouldnotknowifitwastheexperimentaltaskthat madeadifferenceorthetypeofpersonyou dtested. Randomassignmentliterallymeansrandom,itdoesnotmeanthatyoujustdidnothaveanyspecificmethodyoucan put your finger on. If participants are randomly assigned to groups, any significant result you get CANNOT be explainedbyindividualdifferencesthatyoudidnotcontrol.ifyougetasignificantresult,donotsayinyourdiscussion Butwedidn tmeasureiq,thismustinfluencehowwellpeoplecanrememberwordsandperhapsthisexplainsthe significant result. Random assignment means that any characteristic that may differ from one person to another shouldberoughlyequallydistributedacrosstheexperimentalgroups.ofcourse,randomassignmentwillsometimes producealargeexcessofe.g.cleverpeopleinonegroup,butthat sexactlywhatyourpvaluesmeasure:howlikelyis itthatyou dgetthedatathatyouhaveifchanceproducedtheresults.chanceisalwaysatwork,andthat swhatyou arecontrollingbysettingyourpvalues. Experimenter effects Youwillhavemorethanoneexperimenter(becauseyou reworkinginsmallgroups).therefore,eachexperimenter shouldrunthesamenumberofpeopleineachgroupaseveryotherexperimenter.donotsay Ok,I llrunthepeople ingroup1,yourunthepeopleingroup2andsoon.thereasonwhyyoushoulddothisisbecauseofexperimenter0 effects.whotheexperimenteris,theirexpectationsandcharactercanstronglyaffecthowparticipantsperform.even whenallinstructionsarewrittendown,ithasbeenshownthatdifferentexperimenterscanproducedifferentlevelsof performance. Even rats perform differently when different experimenters with different expectations are administeringthetask. Write down your instructions Giveparticipantswritteninstructions.Writingtheinstructionswillhelpyouthinkclearlyabouthowbesttoinstruct people.itwillalsohelpyougiveamorestandarddeliverythroughouttheexperiment. Keep everything constant except for the cover task Inyourexperimentyou llhavedifferentgroupsofpeopledoingdifferenttasks(perhapswithdifferentcoverstories). Do not use different sets of stimuli (most of you will be using words or pictures) for different experimental tasks, otherwiseyouwon tknowifanydifferencebetweenthegroupsisbecausethetasksvariedorbecausethewords varied.forexample,differentwordsaremoreorlesseasytoremember forexample,concretewordsareeasierto rememberthanabstractwords.ifyouareinterestedintheeffectofatask,usethesamestimuliforeachtask.(of course, you might be interested in different types of words then you would use the same experimental task for differentsetsofwords.) Forexample,ifonecovertaskistostatethecolourofthewordsorthelettercasetheyarein,youwillneedwordsof differentcoloursandinupperandlowercase.butthenusethesamestimuliforallgroups.sothegroupthatdoesa semantictaskstillseesthewordsindifferentcolours.bykeepingconstantasmanythingsaspossibleyoucansay morepreciselywhatcouldhavecausedanydifferencesbetweenthegroups. Prof.AndyField,2012 www.discoveringstatistics.com0 Page7

Youshouldalsocontroltheexposuretimeofeachstimulus.Ifyoujustgivepeoplethelistofwordsallatonce,people mighttake2minutestostatethelengthofeachword,but3minutestosaywhatroominahouseitismostlikelyto befound.ifrecallisdifferentbetweenthegroups,isthatbecauseofthetypeofprocessingtheyengagedin,orjust becausetheylookedatthewordslongerinonecaseratherthantheother?youcouldshoweachwordonacardfora setamountoftime,e.g.fiveseconds,togetroundthisproblem. Recency effect Justafteraparticipanthasseenasetofstimuli,thelastfewstimuliwillberememberedalmostperfectly,regardless oftheexperimentaltask.thisisknownastherecencyeffect.therefore,thelastfewstimuliwillnotbeespecially useful in distinguishing the groups if there is a recency effect. To get around this, you could give participants a distractertaskafterthestudyphase(e.g.solvesomemathsproblemsforaminute),ormakesurethatyouusesome distracterstimuliattheendofthestudyphase,sothatthestimuliyou reactuallyinterestedindonotappearatthe endofthisphase. Congruency effect Forexperimentaltasksthatinvolvesayes/noanswer,participantsrememberthosewordsbestthattheygavea yes answertoratherthana no answer.ifparticipantsareclassifyingthestimuliintodifferentcategories,thenumberof categoriescanalsoinfluencerecall.sotrytohavethesamenumberofresponsetypesforeachexperimentaltask,and thesamenumberofstimuliforeachresponsetype.forexample,ifonetaskis Arethewordsinuppercase? you couldhavehalfthewordsinupperandhalfinlowercase.ifanotherquestionis Isitananimal?,havehalfthewords beingananimalandhalfnot. How is memory assessed? Youcoulduseafreerecalltest( Inthenexttwominutes,trytorecallallthewordsyousaw ),orarecognitiontest ( Hereare40words,halfweretheonesyoujustsawandtheotherhalfarenew.Saywhichiswhich. ). How Many people should I test? Youshouldtrytotestatleast10K15peopleineachexperimentalgroup. Pilot experiment Before you run the experiment proper, it is a good idea to run a pilot. Just run a couple of people through the procedure.checkthattheinstructionswereclear,thetimingsareappropriate,andthetasksareneithertooeasynor too difficult. If all goes smoothly you are ready to run; otherwise, alter the procedure and try it on another pilot participant. References Anderson,M.C.,Bjork,R.A.,&Bjork,E.L.(1994).Rememberingcancauseforgetting:RetrievaldynamicsinlongKterm memory.journal0of0experimental0psychology:0learning,0memory,0&0cognition,20,1063k1087. Bartlett,F.C.(1932).Remembering:0A0study0in0experimental0and0social0psychology.NewYork:Macmillan. Burt,C.D.B.,&Popple,J.S.(1996).Effectsofimpliedactionspeedonestimationofeventduration.Applied0Cognitive0 Psychology,10,53K63. Ceci, S. J., & Bruck, M. (1993). Suggestibility of the child witness: A historical review and synthesis. Psychological0 Bulletin,113,403K439. Deese, J. (1959). On the prediction of occurrence of particular verbal intrusions in immediate recall. Journal0 of0 Experimental0Psychology,58,17K22. Garry,M.,Manning,C.G.,Loftus,E.F.,&Sherman,S.J.(1996).Imaginationinflation:Imaginingachildhoodevent inflatesconfidencethatitoccurred.psychonomic0bulletin0&0review,3,208k214. Hilgard,E.R.(1953).Introduction0to0Psychology.NewYork:Harcourt,BraceandCompany. Prof.AndyField,2012 www.discoveringstatistics.com0 Page8

HydeandJenkins(1973).Journal0of0Verbal0Learning0and0Verbal0Behavior,12,471K480. Hyman, I. E., Husband, T. H., & Billings, F. J. (1995). False memories of childhood experiences. Applied0 Cognitive0 Psychology,9,181K197. Loftus, E. F. (1997, September). Creating false memories. Scientific0 American, 277, 70K75. (Available on http://faculty.washington.edu/eloftus/articles/sciam.htm) Loftus,E.F.,Miller,D.G.,&Burns,H.J.(1978).Semanticintegrationofverbalinformationintovisualmemory.Journal0 of0experimental0psychology:0human0learning0and0memory,4,19k31. Loftus, E. F. & Palmer, J. C. (1974). Reconstruction of automobile destruction: An example between language and memory.journal0of0verbal0learning0and0verbal0behavior,13,3k13. Loftus,E.F.,&Pickrell,J.E.(1995).Theformationoffalsememories.Psychiatric0Annals,25,720K725. Mazzoni,G.A.L.,Lombardo,P.,Malvagia,S.&Loftus,E.F.(1999).Dreaminterpretationandfalsebeliefs.Professional0 Psychology:0 Research0 and0 Practice, 30, 45K50. (Available on http://faculty.washington.edu/eloftus/articles/mazz.htm) McCloskey,M.&Zaragoza,M.S.(1985).Misleadingposteventinformationandmemoryforevents:Argumentsand evidenceagainstmemoryimpairmenthypotheses.journal0of0experimental0psychology:0general,114,1k16. Neisser,U.(1967).Cognitive0Psychology.AppletonKCenturyKCrofts:NewYork. Roediger, H. L., & McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal0of0Experimental0Psychology:0Learning0Memory0and0Cognition,21,803K814. Schneider,D.M.,&Watkins,M.J.(1996).Responseconformityinrecognitiontesting.Psychonomic0Bulletin0&0Review, 3,481K485. Wells,G.L.&Bradfield,A.L.(1999).Distortionsineyewitnesses'recollections:Canthepostidentificationfeedback effectbemoderated?psychological0science,10,138k144. Wright,D.B.,Self,G.,&Justice,C.(2000).Memoryconformity:Exploringmisinformationeffectswhenpresentedby anotherperson.british0journal0of0psychology,91,189k202 This0handout0has0evolved0over0many0years0with0contributions0from0Zoltan0Dienes0and0Dan0Wright.& Prof.AndyField,2012 www.discoveringstatistics.com0 Page9