3- population change
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Population Change
Grace T, Cruz, Ph.D
TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Theterm isusuallyusedwhenactually
increaseordecreaseispossible.
Isthedifferencebetweenthesizeof
thepopula:onatdifferentdates.P1
Increase
absolutenumberpercent
P2
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
1. Na:onalandsubna:onalareasmaychange
Areashouldbeconstanttoavoiddiscon>nuity
2. Defini:onsofpopula:ontobecountedmaychange
3.CompletenessofcoveragemayvaryChangeinaccuracy
Dejure
vs.
Defacto
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Rememberthisequa:oninourfirstlecture?
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Thusour(ini:al)popula:onchangesdependingifthereisasurplus(ordeficit)ofbirthsoverdeathsinapopula:onina
given:meperiod
Fromthebalancingequa:on,weseethatone
componentofpopula:onchangeis
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
therateatwhichapopula.onisincreasing(or
decreasing)inagivenyearduetoasurplus(or
deficit)ofbirthsoverdeaths,expressedasthe
percentageofthebasepopula.on
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Arithme3c,Geometric,Exponen3al
Linearchangecompu:ngtheamountof
changeayear,amonth,etc.
Ratesofchangemeasurestheaverage
annualrateofgrowth;more
meaningfulcomparison
TypesofRatesofChange:
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RichvilleHotel,MandaluyongCity
LinearChange
Straighorward Dividethechangebythenumberofyears,months,etc
Assumethatgrowthislinearorfollowsanarithme:cprogression
i.e.,thatthereisaconstantamountofincreaseperunitof>me
compu>ngtheamountof
changeayear,amonth,etc.
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Pn=P0+bn
Generalequa:on
where:
Pn =popula:onattheendoftheperiod,
P0 =theini:alpopula:on,
n =the:meinyears
b =annualamountofchange
compu>ngtheamountofchangeayear,amonth,etc.
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Therateatwhichapopula:onisincreasing(ordecreasing)inagivenyearduetonatural
increaseandnetmigra:on,expressedasapercentageofthebasepopula:on.
Measuresofpopula:onchange Arithme:cgrowthrate Geometricgrowthrate Exponen:algrowthrate
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Pn =popula:onatthelaterperiod
P0 =popula:onattheearlierperiod
n =:meinyears
Arithme:capproxima:on
toanaveragerate
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Ratesarecomparableonlywhentheperiodsareofequallength.
Withunequalperiodsandincreasing
popula:on,thelongerperiodtendsto
havethehighestapproximaterate.
WARNING!
WARNING!
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
e.g.Geometricrateofgrowthbetween1980-1990assumes
thattherateofchangeisconstantthroughouttheperiod
assumesthatthepopula:onincreasesor
decreasesatthesamerateduringeachunit
of:me,usuallyayear.
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Pn = popula:onatthelaterperiod
P0 = popula:onattheearlierperiod
r = annualgrowthratefromP0toPnt = :mebetweenthetwoperiods
Popula:onincreasesordecreaseatthe
samerateovereachunitof:me,for
example,eachyear.
Manipula>ngtheequa>on,we
getthefollowingtosolveforr:
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RichvilleHotel,MandaluyongCity
Geometricchangeiscompounded-interesttype
ofchangeinwhichthecompoundingtakes
placeatcertainconstantintervals(eg.year)
Compoundingisarbitrary.Inthelimi:ngcase,
thecompoundingtakesplacecon:nuously,i.e.
aconstantrateofchangeisappliedatevery
infitesimalof:me.
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Pn =popula:onatthelaterperiod
P0 =popula:onattheearlierperiod
e =exponen:alfunc:on
r =annualgrowthratefromP0toPn
t =:mebetweenthetwoperiods
Manipula>ngtheequa>on,we
getthefollowingtosolveforr:
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity 18
Usingourknowledgeofthe
differentwaysofcomingup
withgrowthrates,wecan
computeforthenumberof
yearsitwouldtakeforour
currentpopula:ontodoubleinsize
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TrainingCourseonBasicDemography
RichvilleHotel,MandaluyongCity
Timetodosome
exercises!
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RichvilleHotel,MandaluyongCity
Census
dates
Population
size
Increase
since
preceding
date
Intercens
al yearsAverage
annual
increase
Doubling
Time
May 1, 1980 48,098,460
May 1, 1990 60,559,116
May 1, 2000 76,498,735
August 1,2007 88,574,614
Canyoufillupthistable?
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Thank You!
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