PORTFOLIO ANALYSIS AND INVESTMENT PAIlecture07 投资组合分析Word文件下载.docx
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Figure2.10LondonStockExchange
Suppose,weareinvestigatingthecaseofsixshares(simulation)withthefollowingmeanandstandarddeviation,respectively:
Figure2.11ReturnandStandarddeviationof6shares
stock
return
St.dev
1
5%
7%
2
6%
9%
3
9%
14%
4
4%
5
3%
6%
6
7%
13%
Fromthisfigureweobservethatthereisatrendaccordingtowhich,higherriskisawardedwithhigherreturns.Supposenow,thatthereexist15investors,eachofwhichconstructsaportfolioconsistingofthesesharesbasedonhisinformationalsetandhisrisktolerance.Thefollowingfigureillustratestheshareweightsthateachinvestorhasutilizedinordertoconstructhisportfolio(i.e.the1stinvestorhasinvestedmostofhismoneyonthe3rdstock,whilethe12thonthe5thstock).
Figure2.12Simulatedportfolios–portfolioweights
Feasibleportfolioset
Itisobviousthattheconstructionofaportfolioisamorecomplicatedissue,sincethereexist,manyshares(notonlysix).Inthefollowingfigurewehaveillustratedthe15portfolio’srisk-returnrelationship,aswellasadashedcurve.Theareabelowthedashedcurverepresentsthesetofallfeasiblerisk-returncombinations(allpossibleportfolios)andiscalledfeasibleportfolioset(FPS).Asitisobvious,theFPScontainsalsothe15investor’schoices.Thus,investorsbasedontheirexpectations,constructportfoliosthatcontributetotheformulationoftherequiredreturnswhichwouldcompensatethemfortherisktheyundertake.Asitisobvious,thereexistsharesthereturnsofwhichdonotaccountforthehighriskleveltheyembed,sufficiently.
Figure2.13FeasiblePortfolioSet
EfficientPortfolioFrontier
Rationalinvestors,whoareriskaverters,wouldpreferportfoliosthereturnofwhichismaximizedforaspecificlevelofrisk,orinversely,wouldpreferportfoliostheriskofwhichisminimizedforaspecifictargetreturn.Thus,rationalinvestors’choicesarerepresentedbythenorth-westpointsoffigure2.13.
Inthecaseofthe6shareswecouldconstruct20differentportfolioswithrespecttothecomponentsoftheportfolio.However,ineachcaseofthe20portfoliostherearemanydifferentcombinationswithrespecttotheshareweightsaninvestoriswillingtoapply.Inthecaseweinvestigatenshareswemayconstructmanyportfoliosofdifferentsizeandforeachoftheseportfoliosthereexistmanyotherchoicesregardingtheshareweights.Allpossiblecombinationsofnsharesthatformulateaportfolioofsizek(k<
n)areequalto:
Thus,areasonablequestioniswhetheraninvestor,shouldconsiderallthesecombinationsbeforeconstructinghisportfolio.TheModernPortfolioTheoryanswersthisproblem,sinceinvestorsshouldnotinvestigateallpossibleportfolios,butinsteadonlythoseportfoliosthatforaspecificlevelofriskofferthemaximumreturn,orinversely,thoseportfoliosthatforaspecifictargetreturnembedthelowerlevelofrisk.Theportfoliosthatfollowthispropertyarecalledefficient,andthecombinationofalltheseefficientportfolios,formstheefficientportfoliofrontier(EPF).
Thus,rationalinvestorswouldformulateanewsetofportfolios,theEfficientPortfolioFrontier,whichisderivedbythefeasibleportfoliosetandsatisfiesthefollowingtwoprinciples:
-foraspecifictargetportfolioreturn,embedsthelowerlevelofrisk(west)
-foraspecificlevelofrisk,offersthehighestportfolioreturn(north)
Morespecifically,investorsinordertoreachtheEPFshouldmoveinthenorth-westdirectionontherisk-returnillustrationofthefeasibleportfolioset.
AllportfoliosthatbelongtotheEPFcontainthehighestleveloftheratioreturn/riskandconsequentlyrepresenttheoptimumchoicesforinvestors.
Figure2.14FeasiblePortfolioSetandtheEfficientPortfolioFrontier
Inthefollowingfigure(Figure2.15)weobservetheEPFandtwootherchoices,pointsKandK’.K’isnotafeasibleportfolio,whileKisnotefficient,sincethereexistotherportfolios(i.e.M,N)thatforthesameportfolioreturnembedlowerrisk,orforthesamelevelofrisktheyofferhigherreturns,respectively.Thus,rationalinvestorsthatareriskaverterswillneverchooseaportfoliointheareabelowtheEPF.Thefinallydecisionoftheinvestorwillbechosensoastomaximizehissatisfaction.
Figure2.15EfficientPortfolioFrontier-EPF
TheEfficientPortfoliosofouranalysisconsistonlyofequities,i.e.financialproductsthatembedrisk.Thus,theslopeofthetangencyoftheEPFcurverepresentstheextrariskthatinvestorsarewillingtoundertakeforamarginalincrementontheirportfolios’returns.AllportfoliosontheEPFhavethemaximumreturn/riskratio.
Optimumportfolio
Asitisknowtheutilityfunctionofariskaverterexpressedonthefirsttwomomentsisconvex,andeveryinvestoriswillingtomaximizehisutility.
Figure2.16Riskaverterprofile(convexfunction)
Byconsiderationoftheutilityfunctionintheinvestigationofaportfoliochoice,thereexistaportfolioontheEPFforwhichinvestor’sutilityismaximized.Thisportfolio(A)iscalledoptimum,sinceitofferstheinvestorthemaximumexpectedutilityamongallEPFportfoliosandisidentifiedatthepointatwhichtheslopeoftheutilityfunctionisequaltotheslopeoftheEPF,asshownonFigure2.17.
Figure2.17OptimumPortfolio
However,theutilityfunctionisalocusthatexpressestheindividualinvestor’sexpectationsandasaresulttheoptimumportfolioshouldbedifferentamonginvestors.
Foramoreriskaverterinvestor(U1)theoptimumportfolioisAwhileforalessriskaverterinvestor(U2)theoptimumportfolioisB,asillustratedbelow:
Figure2.18Optimumportfoliosfortworiskaverterinvestors(withdifferentrisktolerance)
-AswehavealreadyseentheconcavityoftheEPFdependsonthecorrelationstructureoftheequityreturns,inversely,andasaresultlowercorrelationstructureofassetreturnswouldmaximizeinvestor’ssatisfaction.
Diversification
Theportfoliovarianceisgivenbythefollowingequation:
Alternatively,byisolatingtheelementsofthemaindiagonalofthevar-covariancematrixweget:
Assumingthatallshareshavethesamevariance(σ2),thateachpairofshareshasthesamecovariance(cov)andthattheallsharesintheportfoliohavethesameweight(w=1/n)thenweget:
Thisrelationshipimpliesthatasthesizeoftheportfolioisincreased(n∞)thecontributionofindividualsharesontheportfoliovariance,isdecreased,sincetheportfoliovariancedependsmainlyonthecovariancebetweenshares’returns.
Figure2.19Portfoliosizeanddiversification
Asthenumberofsharesontheportfolioisincreasedtheidiosyncraticriskofeachshareisomitted(diversified),whilethesystematicriskisnotaffected.
-idiosyncraticrisk:
Itisthepartoftheriskofashare,duetothespecificcharacteristicsofthecorrespondinglistedfirm,suchasthemanagement,thetechnologicalfactors,theequipment,thesectorandmanyotherfactorsandiscalledidiosyncraticorspecificornonsystematicrisk.Whenashareisincludedinthemarketportfolio,partoftheshare’sriskisgoingtobeomittedgiventhatthecorrelationcoefficientofthereturnsoftheshareandthemarketportfolioislow.Thisportionofshareriskisnotofinterestwhendealingwithwelldiversifiedportfolios,inthesensethatunanticipatedlossesfromoneshareontheportfolioarehedgedbythegainsofanotherone.
-systematicrisk
Itisthepartoftheriskofashare,duetothecovariancebetweentheportfolio’sshares.Morespecifically,itisthepartoftheriskthatisundiversifiablebecauseitisassociatedwithmanyfinancialandmacroeconomicvariables(thenationalorinternationalpoliticalregime,theinflation,themonetarypolicy,thetaxpolicy,thelevelofinterestrates,theinvestors’expectationsaboutfutureeconomicstates)andiscalledsystematicormarketrisk.Thispartoftheriskisundiversifiableandallinvestorsshouldundertakethiswhenincludingthissharetotheirportfolios.
Thus,financialmarketsdorewardinvestorsonlyforthesystematicriskofshares,sincethespecificriskcouldbeeliminatedinawelldiversifiedportfolio.Inadevelopedandcompletefinancialmarket,investorsshouldconsideronlythesystematicriskintheformulationoftheirportfolios,becauseonlythispartofshares’riskisnotomittedinawelldiversifiedportfolio.
(totalrisk)=(systematicrisk)+(specificrisk)
LendingandBorrowingopportunitiesandtheCapitalMarketLine
Supposenow,thataninvestorcouldinvestonequity(shares)andrisklessassets,suchasgovernmentbonds(rf).Thefixedincomesecuritiesembednoriskwhichmeansthattheirstandarddeviationaswellastheircorrelationorcovariancewithotherrandomvariablesisequalwithzero.
Now,s