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1、DecisionSciencesVolume35Number1Winter2004PrintedintheU.S.A.TheEffectofLeadTimeUncertaintyonSafetyStocksSunilChopraKelloggGraduateSchoolofManagement,NorthwesternUniversity,Evanston,IL,60201,e-mail:s-chopra@kellogg.northwestern.eduGillesReinhardt†Departmento
2、fManagement,DePaulUniversity,Chicago,IL,60604,e-mail:greinhar@condor.depaul.eduMaqboolDadaKrannertGraduateSchoolofManagement,PurdueUniversity,WestLafayette,IN,47907,e-mail:dada@mgmt.purdue.eduABSTRACTThepressuretoreduceinventoryinvestmentsinsupplychainshas
3、increasedascompeti-tionexpandsandproductvarietygrows.Managersarelookingforareastheycanimprovetoreduceinventorieswithouthurtingthelevelofserviceprovided.Twoareasthatman-agersfocusonarethereductionofthereplenishmentleadtimefromsuppliersandthevariabilityofthi
4、sleadtime.Thenormalapproximationofleadtimedemanddistributionindicatesthatbothactionsreduceinventoriesforcycleservicelevelsabove50%.Thenormalapproximationalsoindicatesthatreducingleadtimevariabilitytendstohaveagreaterimpactthanreducingleadtimes,especiallywh
5、enleadtimevariabilityislarge.WebuildontheworkofEppenandMartin(1988)toshowthattheconclusionsfromthenormalapproximationareflawed,especiallyintherangeofservicelevelswheremostcompaniesoperate.Weshowtheexistenceofaservice-levelthresholdgreaterthan50%belowwhichre
6、orderpointsincreasewithadecreaseinleadtimevariability.Thus,forafirmoperatingjustbelowthisthreshold,reducingleadtimesdecreasesreorderpoints,whereasreducingleadtimevariabilityincreasesreorderpoints.Forfirmsoperatingattheseservicelevels,decreasingleadtimeisther
7、ightleveriftheywanttocutinventories,notreducingleadtimevariability.SubjectAreas:InventoryManagement,MathematicalProgramming/Optimization,ProbabilityModelsandSupplyChainManagement.INTRODUCTIONANDFRAMEWORKManagershavebeenunderincreasingpressuretodecreaseinve
8、ntoriesassupplychainsattempttobecomeleaner.Thegoal,however,istoreduceinventorieswithouthurtingthelevelofserviceprovidedtocustomers.Safetystockisafunctionofthecycleservicelevel,thedemanduncertainty,thereplenis
