伍德里奇计量经济学英文版各章总结K12教育文档.docx
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伍德里奇计量经济学英文版各章总结K12教育文档
伍德里奇计量经济学英文版各章总结(word版可编辑修改)
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CHAPTER1
TEACHINGNOTES
YouhavesubstantiallatitudeaboutwhattoemphasizeinChapter1。
Ifinditusefultotalkabouttheeconomicsofcrimeexample(Example1.1)andthewageexample(Example1.2)sothatstudentssee,attheoutset,thateconometricsislinkedtoeconomicreasoning,eveniftheeconomicsisnotcomplicatedtheory.
Iliketofamiliarizestudentswiththeimportantdatastructuresthatempiricaleconomistsuse,focusingprimarilyoncross—sectionalandtimeseriesdatasets,asthesearewhatIcoverinafirst—semestercourse.Itisprobablyagoodideatomentionthegrowingimportanceofdatasetsthathavebothacross—sectionalandtimedimension。
Ispendalmostanentirelecturetalkingabouttheproblemsinherentindrawingcausalinferencesinthesocialsciences.Idothismostlythroughtheagriculturalyield,returntoeducation,andcrimeexamples.Theseexamplesalsocontrastexperimentalandnonexperimental(observational)data。
Studentsstudyingbusinessandfinancetendtofindthetermstructureofinterestratesexamplemorerelevant,althoughtheissuethereistestingtheimplicationofasimpletheory,asopposedtoinferringcausality。
Ihavefoundthatspendingtimetalkingabouttheseexamples,inplaceofaformalreviewofprobabilityandstatistics,ismoresuccessful(andmoreenjoyableforthestudentsandme)。
CHAPTER2
TEACHINGNOTES
ThisisthechapterwhereIexpectstudentstofollowmost,ifnotall,ofthealgebraicderivations。
InclassIliketoderiveatleasttheunbiasednessoftheOLSslopecoefficient,andusuallyIderivethevariance。
Ataminimum,Italkaboutthefactorsaffectingthevariance.Tosimplifythenotation,afterIemphasizetheassumptionsinthepopulationmodel,andassumerandomsampling,Ijustconditiononthevaluesoftheexplanatoryvariablesinthesample.Technically,thisisjustifiedbyrandomsamplingbecause,forexample,E(ui|x1,x2,…,xn)=E(ui|xi)byindependentsampling。
IfindthatstudentsareabletofocusonthekeyassumptionSLR.4andsubsequentlytakemywordabouthowconditioningontheindependentvariablesinthesampleisharmless.(Ifyouprefer,theappendixtoChapter3doestheconditioningargumentcarefully。
)Becausestatisticalinferenceisnomoredifficultinmultipleregressionthaninsimpleregression,IpostponeinferenceuntilChapter4.(Thisreducesredundancyandallowsyoutofocusontheinterpretivedifferencesbetweensimpleandmultipleregression。
)
Youmightnoticehow,comparedwithmostothertexts,IuserelativelyfewassumptionstoderivetheunbiasednessoftheOLSslopeestimator,followedbytheformulaforitsvariance。
ThisisbecauseIdonotintroduceredundantorunnecessaryassumptions.Forexample,onceSLR.4isassumed,nothingfurtherabouttherelationshipbetweenuandxisneededtoobtaintheunbiasednessofOLSunderrandomsampling.
CHAPTER3
TEACHINGNOTES
Forundergraduates,Idonotworkthroughmostofthederivationsinthischapter,atleastnotindetail。
Rather,Ifocusoninterpretingtheassumptions,whichmostlyconcernthepopulation.Otherthanrandomsampling,theonlyassumptionthatinvolvesmorethanpopulationconsiderationsistheassumptionaboutnoperfectcollinearity,wherethepossibilityofperfectcollinearityinthesample(evenifitdoesnotoccurinthepopulation)shouldbetouchedon.Themoreimportantissueisperfectcollinearityinthepopulation,butthisisfairlyeasytodispensewithviaexamples。
Thesecomefrommyexperienceswiththekindsofmodelspecificationissuesthatbeginnershavetroublewith。
Thecomparisonofsimpleandmultipleregressionestimates–basedontheparticularsampleathand,asopposedtotheirstatisticalproperties –usuallymakesastrongimpression.SometimesIdonotbotherwiththe“partiallingout”interpretationofmultipleregression。
Asfarasstatisticalproperties,noticehowItreattheproblemofincludinganirrelevantvariable:
noseparatederivationisneeded,astheresultfollowsformTheorem3.1。
Idoliketoderivetheomittedvariablebiasinthesimplecase.ThisisnotmuchmoredifficultthanshowingunbiasednessofOLSinthesimpleregressioncaseunderthefirstfourGauss-Markovassumptions。
Itisimportanttogetthestudentsthinkingaboutthisproblemearlyon,andbeforetoomanyadditional(unnecessary)assumptionshavebeenintroduced.
Ihaveintentionallykeptthediscussionofmulticollinearitytoaminimum.Thispartlyindicatesmybias,butitalsoreflectsreality。
Itis,ofcourse,veryimportantforstudentstounderstandthepotentialconsequencesofhavinghighlycorrelatedindependentvariables。
Butthisisoftenbeyondourcontrol,exceptthatwecanasklessofourmultipleregressionanalysis。
Iftwoormoreexplanatoryvariablesarehighlycorrelatedinthesample,weshouldnotexpecttopreciselyestimatetheirceterisparibuseffectsinthepopulation.
Ifindextensivetreatmentsofmulticollinearity,whereone“tests"orsomehow“solves"themulticollinearityproblem,tobemisleading,atbest。
EventheorganizationofsometextsgivestheimpressionthatimperfectmulticollinearityissomehowaviolationoftheGauss—Markovassumptions:
theyincludemulticollinearityinachapterorpartofthebookdevotedto“violationofthebasicassumptions,”orsomethinglikethat。
Ihavenoticedthatmaster'sstudentswhohavehadsomeundergraduateeconometricsareoftenconfusedonthemulticollinearityissue.Itisveryimportantthatstudentsnotconfusemulticollinearityamongtheincludedexplanatoryvariablesinaregressionmodelwiththebiascausedbyomittinganimportantvariable.
IdonotprovetheGauss—Markovtheorem.Instead,Iemphasizeitsimplications。
Sometimes,andcertainlyforadvancedbeginners,IputaspecialcaseofProblem3。
12onamidtermexam,whereImakeaparticularchoiceforthefunctiong(x).Ratherthanhavethestudentsdirectlycomparethevariances,theyshouldappealtotheGauss-MarkovtheoremforthesuperiorityofOLSoveranyotherlinear,unbiasedestimator。
CHAPTER4
TEACHINGNOTES
AtthestartofthischapterisgoodtimetoremindstudentsthataspecificerrordistributionplayednoroleintheresultsofChapter3.ThatisbecauseonlythefirsttwomomentswerederivedunderthefullsetofGauss-Markovassumptions。
Nevertheless,normalityisneededtoobtainexactnormalsamplingdistributions(conditionalontheexplanatoryvariables).IemphasizethatthefullsetofCLMassumptionsareusedinthischapter,butthatinChapter5werelaxthenormalityassumptionandstillperformapproximatelyvalidinference.Onecouldarguethattheclassicallinearmodelresultscouldbeskippedentirely,andthatonlylarge—sampleanalysisisneeded。
But,fromapracticalperspective,studentsstillneedtoknowwherethetdistributioncomesfrombecausevirtuallyallregressionpackagesreporttstatisticsandobtainp—valuesoffofthetdistribution。
IthenfinditveryeasytocoverChapter5quickly,byjustsayingwecandropnormalityandstillusetstatisticsandtheassociatedp—valuesasbeingapproximatelyvalid。
Besides,occasionallystudentswillhavetoanalyzesmallerdatasets,especiallyiftheydotheirownsmallsurveysforatermproject.
Itiscrucialtoemphasizethatwetesthypothesesaboutunknownpopulationparameters。
ItellmystudentsthattheywillbepunishediftheywritesomethinglikeH0:
=0onanexamor,evenworse,H0:
。
632=0。
OneusefulfeatureofChapter4isitsillustrationofhowtorewriteapopulationmodelsothatitcontainstheparameterofinterestintestingasinglerestriction。
Ifindthisiseasier,boththeoreticallyandpractically,thancomputingvariancesthatcan,insomecases,dependonnumerouscovarianceterms.Theexampleoftestingequalityofthereturntotwo-andfour—yearcollegesillustratesthebasicmethod,andshowsthattherespecifiedmodelcanhaveausefulinterpretation.Ofcourse,somestatisticalpackagesnowprovideastandarderrorforlinearcombinationsofestimateswithasimplecommand,andthatshouldbetaught,too.
OnecanuseanFtestforsinglelinearrestrictionsonmultipleparameters,butthisislesstransparentthanattestanddoesnotimmediatelyproducethestandarderrorneededforaconfidenceintervalorfortestingaone-sidedalternative。
Thetrickofrewritingthepopulationmodelisusefulinseveralinstances,includingobtainingconfidenceintervalsforpredictionsinChapter6,aswellasforobtainingconfidenceintervalsformarginaleffectsinmodelswithinteractions(alsoinChapter6)。
Themajorleaguebaseballplayersalaryexampleillustratesthedifferencebetweenindividualandjointsignificancewhenexplanatoryvariables(rbisyrandhrunsyrinthiscase)arehighlycorrelated。
ItendtoemphasizetheR-squaredformoftheFstatisticbecause,inpractice,itisapplicablealargepercentageofthetime,anditismuchmorereadilycomputed。
Idoregretthatthisexampleisbiasedtowardstudentsincountrieswherebaseballisplayed.Still,itisoneofthebetterexamplesofmulticollinearitythatIhavecomeacross,andstudentsofallbackgroundsseemtogetthepoint。
CHAPTER5
TEACHINGNOTES
Chapter5isshort,butitisconceptuallymoredifficultthantheearlierchapters,primarilybecauseitrequiressomeknowledgeofasymptoticpropertiesofestimators.Inclass,Igiveabrief,heuristicdescriptionofconsistencyandasym