Basic-statistics.ppt

Basic-statistics.ppt

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Basicstatistics,郜战莹外国语言学及应用语言学硕士研究生,ContentAbriefdescriptionofstatisticsDescriptionstatisticsInferentialstatistics,1.Abriefdescriptionofstatistics1.1Definitions1.2Twoimportantterms,1.1,Definitions,descriptivestatistics,inferentialstatistics,1.1.1DescriptivestatisticsIfareseacherisinterestedonlyindescribingagroupfromwhichthedataaregathered,thestatisticsinvolvediscalleddescriptivestatistics.Note:

Inmanycasesdatainthefieldofappliedlinguisticsarepriamrilydescriptiveinnature.,1.1.2InferentialstatisticsIfhisorherinterestgoesbeyonddescribingthegroupfromwhichthedataarecollectedands/hetriestodrawconclusionsaboutthepopulationfromwhichthegroupwasselected,thestatisticsneededinthiscaseininferentialstatistics.Note:

Itsadvantageistoallowthereseachertomakedecisionsaboutthepopulationwithoutstudyingtheentirepopulation.,1.2,Twoterms,parameter,statistic,Parameterisadescriptivemeasureofthepopulation,whichisdenotedbyGreekletterssuchasPage180.e.g:

populationmeanpopulationvariancepopulationstandarddeviation,Parameter,Statisticisadescriptivemeasureofasample,whichisdenotedbyaRomanletter,suchastheexamplesinpage180e.g.samplemeansamplevariancesamplestandarizationdeviation,Statistic,Diferentiationbetweenparameterandstatisticisimportantonlyintheuseofinferentialstatistics.Thestatisticianoftenwantstoestimatethevalueofaparameter.However,therearesomefactorscanaffectthevalues,especially:

Note,time,money,Anexample:

SupposeyouareanEnglishteacheratNanjingUniversityandyouwanttoknowtherelationshipbetweentheuseofstrategiesandtheEnglishproficiencyofalltheNanjingUniversitystudents.Therearemorethan10,000studentsontwocampuses.Obviously,youcannnotaffordthemoneyandtimetotakeacensus.Whatyoumaydoistosurvey400studentsasasamplebyaquestionnaire.Then,howdowedo?

descriptivestatisticsinferentialstatistics,Youusedescriptivestatisticstogettoknowwhichstrategiesaremorefrequentlyusedbythese400students.Theresultsyouhavegotareonsample.YoumayuseinferentialstatisticstoexaminetherelationbewteentheuseofstrategiesandEnglishachievement,ortoseewhetherthemalestudentsdifferfromthefemalestudentsintheiruseofstategiesbasedonthenotionprobability,Descriptiveanalysisorstatisticsdescribesthegeneralpatternortendencyemergingfromthedatacollected.Inferentialanalysisorstatistics,morecomplicatedthandescriptive,aimsatpredictionsbeyondthesampledata.,Conclusion,Frequencies,Thesimplestwaytoorganizethedataistodescribetheirfrequencydistributionwhichcanreduceandsummarizedataeffectivelyandefficiently.,frequencydistribution,bargraph,polygon,piechart,Ifthetotalpossiblevaluesareverylimited.,forexample:

ifthestudentsresponsestoquestionnaireitemsarenomorethanfive:

1,2,3,4,5,frequencydistributioncanbeobtainedsimplybytallyingupalltheresponses,asshownintable1.,Table1:

Frequencydistribution,Ifthetotalpossiblevaluesarevarious,suchaspeoplesageandstudentstestscores,weneedtogrouptherawdataintoclasses.,Inthiscase,thefrequencydistributionisconcernedwithclassesratherthanwitheachindividualscore.Howdowedescribethefrequencydistributionintermsofclasses?

Therearenohard-and-fastrulestofollow.,Generallyspeaking,wemayconstructthefrequencydistributionofthesedatainthreesteps:

1.Determinetherangeoftherawdata,2.Determinethenumberoftheclasses,3.Determinethewidthoftheclassinterval,58,65,84,70,90,75,86,76,80,82,83,84,69,84,85,86,72,89,75,92,Attention,1.Therangeoftherawdata:

definedasthedifferencebetweenthelargestandsmallestnumbers.,2.Thenumberofclasses,toomany:

cannotachievegeneralizationtoofew:

cannotseetheimportantdifferences,theappropriatenumberofclasses,between5and10,92-58=34,Attention,range3.thewidthoftheclassinterval=thenumberofclasses组距=全距/组数,Asusual,itis5,10,15andsoon.,4.Thefrequencydistributionmustincludeallthedatagiven.Therefore,thefrequencydistributionshouldstart:

atavalueequaltoorlowerthanthelowestnumberoftheungroupeddataend:

atavalueequaltoorhigherthanthehighestnumber.,Table2:

Frequencydistributionintermsoffiveclasses,Table3:

Frequencydistributionintermsofthreeclasses,Ifyouwanttoknowtherelativestandingofanyparticularscoreinagroupofscores,youcanshowitbyapercentilescore.,formula:

CumulativeFPercentile=（100）N,1.Cumulativefrequency（F）:

referstothefrequencyofthescoreorthescoreswithintheclassjustbelow.2.N:

representsthetotalnumbelofscores.3.Percentile:

definedasanumberwhichrepresentsthepercentofscoresthataparticularrawscoreexceeds.,Table4:

Frequencydistributionwithcumulativefrequenciesandpercenta