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Population Change

Grace T, Cruz, Ph.D

TrainingCourseonBasicDemography

RichvilleHotel,MandaluyongCity

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TrainingCourseonBasicDemography

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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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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

11

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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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TrainingCourseonBasicDemography

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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TrainingCourseonBasicDemography

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!