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1、TheUseofPhase-TypeModelsforDisabilityInsuranceCalculationsAminHassanZadeh1BruceL.JonesandDavidA.StanfordDepartmentofStatisticalandActuarialSciences,UniversityofWesternOntario,London,OntarioN6A5B7,Canada.April19,2010AbstractThispaperexplorestheuseofphase-typemodelsinactuarialcalculationsfordi
2、sabilityinsurance.Wedemonstratethatthechangesinstatusofdis-abilityinsuredscanbeappropriatelycapturedbyaphase-typemodel.Ourmodelrepresentstheagingprocessasthepassagethroughanumberofphasesofdecreasingvitality.Whendisabled,individualsadditionallypassthroughseveralstagesthatrepresentdurationofdi
3、sability.Recoveryandmortalityratesfromtheearlierstagesaregreaterthanthoseinlaterstages.Usingsuchamodel,explicitandeasilycalculableexpressionsareobtainedforrelevantprobabilitiesandactuarialpresentvalues.Thisfacilitatesthecalculationofpremiumsandreserves.Keywords:Actuarialpresentvalue,aggregat
4、eMarkovchain,continuous-timeMarkovchain,disabilityinsurance,phase-typedistribution1Correspondingauthor;e-mail:jones@stats.uwo.ca;tel:(519)661-3149;fax:(519)661-3813.11.IntroductionVarioustypesofdisabilitybenefitsareprovidedbyavarietyofdifferentkindsofinsurancepolicies.Thecommonalityisthatcover
5、edindividualsmayatanytimebeinoneoftwostatuses:active(notdisabled),ordisabled.Thedefinitionofdisabilityisbasedontheindividual’sinabilitytoperformoccupationalduties.Benefitsaretypicallypayableperiodicallywhiletheindividualisinthedisabledstatus,afterawaitingperiod.Actuarialcalculationsfordisabili
6、tycoveragespresentchallengesbecauseofthepos-sibilityofrepeatvisitstothedisabledstatus.Traditionalapproachesinvolvetheuseofdisabilityincidenceratesandterminationrates(see,forexample,Bowersetal.[2],p.359).Theincidenceratesdependonage,andtheterminationratesdependondura-tionofdisabilityandage.Th
7、esesetsofratesallowinsurerstocalculatetheprobabilitythatadisabilitybeginsinagivenyearandcontinuesforagivenperiodoftime.Oftentheterminationratesdonotdistinguishrecoveriesfromdeaths,andthereforecalcula-tionsmayonlycontemplateonespellofdisability.Allo