Aging of Population.docx
- 文档编号:10571817
- 上传时间:2023-02-21
- 格式:DOCX
- 页数:15
- 大小:120.79KB
Aging of Population.docx
《Aging of Population.docx》由会员分享,可在线阅读,更多相关《Aging of Population.docx(15页珍藏版)》请在冰豆网上搜索。
AgingofPopulation
AgingofPopulation
LeonidA.GavrilovandPatrickHeuveline
ThisisamanuscriptofourarticleinTheEncyclopediaofPopulation.NewYork,MacmillanReferenceUSA,2003.
[Note:
Thisoriginalmanuscriptisslightlydifferentfromthefinalpublicationbecauseofsmalleditorialchanges.]
Referencetothepublishedarticle:
GavrilovL.A.,HeuvelineP.
“AgingofPopulation.”
In:
PaulDemenyandGeoffreyMcNicoll(Eds.)
TheEncyclopediaofPopulation.NewYork,MacmillanReferenceUSA,2003
Availableat:
Agingofpopulation(alsoknownasdemographicaging,andpopulationaging)isasummarytermforshiftsintheagedistribution(i.e.,agestructure)ofapopulationtowardolderages. Adirectconsequenceoftheongoingglobalfertilitytransition(decline)andofmortalitydeclineatolderages,populationagingisexpectedtobeamongthemostprominentglobaldemographictrendsofthe21stcentury.Populationagingisprogressingrapidlyinmanyindustrializedcountries,butthosedevelopingcountrieswhosefertilitydeclinesbeganrelativelyearlyalsoareexperiencingrapidincreasesintheirproportionofelderlypeople.Thispatternisexpectedtocontinueoverthenextfewdecades,eventuallyaffectingtheentireworld. Populationaginghasmanyimportantsocio-economicandhealthconsequences,includingtheincreaseintheold-agedependencyratio. Itpresentschallengesforpublichealth(concernsoverpossiblebankruptcyofMedicareandrelatedprograms)aswellasforeconomicdevelopment(shrinkingandagingoflaborforce,possiblebankruptcyofsocialsecuritysystems).
Definingandmeasuringpopulationaging
Asthestudyofpopulationagingisoftendrivenbyaconcernoveritsburdeningofretirementsystems,theagingofpopulationisoftenmeasuredbyincreasesinthepercentageofelderlypeopleofretirementages.Thedefinitionofretirementagesmayvarybutatypicalcutoffis65years,andnowadaysasocietyisconsideredrelativelyoldwhenthefractionofthepopulationaged65andoverexceeds8-10%.Bythisstandard,thepercentageofelderlypeopleintheUnitedStatesstoodat12.6%in2000,comparedwithonly4.1%in1900andaprojectedincreaseto20%bytheyear2030.
Arelatedmeasureofpopulationagingistheelderlydependencyratio(EDR):
thenumberofindividualsofretirementagescomparedtothenumberofthoseofworkingages.Forconvenience,workingagesmaybeassumedtostartatage15,althoughincreasingproportionsofindividualspursuetheireducationbeyondthatageandremain,meanwhile,financiallydependent,eitheronthestateor,increasingly,ontheirparentsorbankmanagers.Theratiooftheelderlydependentpopulationtotheeconomicallyactive(working)populationisalsoknownasold-agedependencyratio,age-dependencyratioorelderlydependencyburdenandisusedtoassessintergenerationaltransfers,taxationpolicies,andsavingbehavior.
Anotherindicatoroftheagestructureistheagingindex(sometimesreferredtoastheelder-childratio),definedasthenumberofpeopleaged65andoverper100youthsunderage15.In2000,onlyafewcountries(Germany,Greece,Italy,Bulgaria,andJapan)hadmoreelderlythanyouth(agingindexabove100).By2030,however,theagingindexisprojectedtoexceed100inalldevelopedcountries,andtheindexofseveralEuropeancountriesandJapanareevenexpectedtoexceed200.Todate,agingindexesaremuchlowerindevelopingcountriesthaninthedevelopedworld,buttheproportionalriseintheagingindexindevelopingcountriesisexpectedtobegreaterthanindevelopedcountries.
Theseindicatorsofpopulationagingaremerehead-countratios(HCR),thatis,theysimplyrelatethenumberofindividualsinlargeagecategories.Theseindicatorsfailtotakeintoaccounttheagedistributionwithintheselargecategories,inparticularamongtheelderly.Whenthefertilityandmortalitytrendsresponsibleforpopulationaginghavebeenfairlyregularovertime,thepopulationgrowthispositivelycorrelatedwithage(i.e.,theoldestagegroupsaregrowingfastest).Thisimpliesthatiftheproportionofthepopulationoverage65isincreasing,withinthat65-and-overpopulationtheproportionover,say,age80isalsoincreasing.Ashealth,financialsituation,andconsumptionpatternsmayvarygreatlybetween65year-oldsand80year-olds,simpleratiosconcealimportantheterogeneityintheelderlypopulation.Increasingly,attentionispaidtothe"oldestolds"(typicallyage80andover).Along-timesubjectofcuriosity,thenumberofcentenariansisgrowingevenfaster.Estimatedat180,000worldwidein2000,itcouldreach1millionby2030(UnitedNations2001).
Thesecondclassofindicatorsforpopulationagingisthegroupofstatisticalmeasuresoflocation(median,meanandmodalagesofpopulation).Themedianage--theageatwhichexactlyhalfthepopulationisolderandanotherhalfisyounger--isperhapsthemostwidelyusedindicator.Fortheyear2000,themedianageintheUnitedStateswas36years,atypicalageformostdevelopedcountriesandtwicethemedianageforAfrica(UnitedNations2001).Becauseitismoresensitivetochangesattheright-handtailoftheagedistribution(i.e.,theoldestoldages),themeanageofpopulationmightinfactbepreferredtothemedianagetostudythedynamicsofpopulationaging.
Sincepopulationagingreferstochangesintheentireagedistribution,anysingleindicatormightappearinsufficienttomeasureit.Theagedistributionofpopulationisoftenveryirregular,reflectingthescarsofthepastevents(wars,depressionetc.),anditcannotbedescribedjustbyonenumberwithoutsignificantlossofinformation.Weretheagedistributiontochangeinaveryirregularfashionovertheagerange,forinstance,muchinformationwouldbelostbyasingle-indexsummary.Therefore,perhapsthemostadequateapproachtostudypopulationagingistoexploretheagedistributionthroughasetofpercentiles,orgraphicallybyanalyzingthepopulationpyramids.Demographerscommonlyusepopulationpyramidstodescribebothageandsexdistributionsofpopulations.Youthfulpopulationsarerepresentedbypyramidswithabroadbaseofyoungchildrenandanarrowapexofolderpeople,whileolderpopulationsarecharacterizedbymoreuniformnumbersofpeopleintheagecategories.
Figures1-5AboutHere
Demographicdeterminantsofpopulationaging
Tounderstandthedemographicfactorsthatcausepopulationaging,demographersoftenrefertostablepopulations(Prestonetal.2001).Thispopulationmodelassumesthatage-specificfertilityandmortalityratesremainconstantovertime,andthisresultsinapopulationwithanagedistributionthatstabilizesandeventuallybecomestimeinvariantaswell.Conversely,thistheoreticalmodelsuggeststhatanychangeinagestructure,andpopulationaginginparticular,canonlybecausedbychangesinfertilityandmortalityrates.Theinfluenceofchangesinfertilityratesonpopulationagingisperhapslessintuitivethanthatofmortalityrates.Everythingelseconstant,however,afertilitydeclinereducesthesizeofthemostrecentbirthcohortsrelativetothepreviousbirthcohorts,hencereducingthesizeoftheyoungestagegroupsrelativetothatoftheolderones.
Theeffectsofchangesinmortalityratesonpopulationagingappearmoreintuitive,butareinfactmoreambiguous.Ifincreasesinthehumanlifespanarecorrectlylinkedtopopulationaging,reductionsinmortalityratesdonotnecessarilycontributetopopulationaging.Morespecifically,mortalitydeclinesamonginfants,childrenandpersonsyoungerthanthepopulationmeanagetendtolowerthepopulationmeanage. Amomentofthoughtsuggeststhatindeedareductionofneonatalmortality(i.e.,deathinthefirstmonthoflife)addsindividualatage0andshouldleadtothesamepartialalleviationofpopulationagingasanincreaseinchildbearing.
Populationagingisthusrelatedtothedemographictransition,thatistheprocessesthatleadasocietyfromademographicregimecharacterizedbyhighratesoffertilityandmortalitytoanotheronewithlowerfertilityandmortalityrates.Inthecourseofthistransition,theagestructureissubjectedtodifferentinfluences.Inthetypicalsequence,thetransitionbeginswithsuccessesinpreventinginfectiousandparasiticdiseasesthatbenefitinfantsandyoungchildrenmost.Theresultingimprovementinlifeexpectancyatbirthoccurswhilefertilitytendstoremainunchanged,therebyproducinglargebirthcohortsandanexpandingproportionofchildrenrelativetoadults.Otherthingsbeingequal,thisinitialdeclineinmortalitygeneratesayoungerpopulationagestructure.
Afterinitialandsometimesveryrapidgainsininfantandchildmortalityhavebeenachieved,furthermortalitydeclinesincreasinglybenefitolderagesandareeventuallyaccompaniedbyfertilitydeclines.Bothchangescontributetoreversetheearlyeffectofmortalitydeclineontheagestructure,andthissynergyisknownasthedoubleagingprocess.Thiscorrespondstotheexperienceofmostdevelopedcountriestoday,butfurtherdecompositionsuggestthattheirhistoryofdecliningmortalityisthedominantfactorincurrentaging(Preston,HimesandEggers1989).Mortalitydeclinescontinueinthesecountriesandthedecreaseinmortalityratesamongtheoldest-old(85+years)hasactuallyacceleratedsincethe1950s(Gavrilov,Gavrilova,1991).Thislatestphaseofmortalitydecline,whichisconcentratedintheolderagegroups,isbecominganimportantdeterminantofpopulati
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Aging of Population