The document discusses crude birth rate and factors that influence population growth rates. It defines crude birth rate as the number of births per 1000 people per year. Crude birth rate minus crude death rate equals the rate of natural increase. Birth rates range from 10-20 births per 1000 being considered low and 40-50 being high. Factors that affect birth rates include government policies, availability of family planning services, economic conditions, education levels and urbanization. The total fertility rate is also discussed, which is the average number of children born to a woman over her lifetime.

1. By Dr. Apsara Nishshanka
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2. The crude birth rate
 Definition:
No. of births per 1000 people per year (natality)
 Measurement method:
CBR=No of births in a given year, during a given time period
(calander year) / Total population* 1000
 Crude birth rate - crude death rate = The rate of natural increase(RNI)
 This is also equal to the rate of population change in the absence of migration.
 we can show this Age specially as well.
( No of births per thousand persons in an Age group)
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3. Birth rate
 The birth rate is typically the rate of births in a
population over a time
In 2012 the average global birth rate was 20.15 (births
for 1000 total population)
It was 20.09 in the year 2007
Birth rates ranging from 10-20 births per 1000 are
considered low
40-50 considered high
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4. Government population policy, such as pronatalist or
antinaterlist policies (eg.Tax on childlessness)
Availability of family planning services, such as birth control &
sex education
Availability & safety of abortion & the safety of child birth
Infant mortality rate
Existing Age –sex structure
Typical Age of marriage
Social religious beliefs especially in relation to contraception and
abortion
Industrialization
Economic prosperity or economic difficulty;(In economic
difficulty times couples delay child bearing
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5.  Poverty levels
Urbanization
Pension availability
Conflict
Illiteracy & un employment
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6. Demographic transition
 DT refers to the decline in population mortality & fertility
decline with social and economic development
 The 2 major factors affecting DT are the CBR & CDR
 The CBR in S/L was 18.16 in 2010 (WBR-2012)
 In pre industrial time high birth and death rates, then the birth
rate was almost constant for a certain period of time while
death rate was reducing .and then be constant it as well (due to
better sanitation & health care)
 After that transitional period, at the post industrial time both
birth & death rates are become low and almost constant.
 In S/L specially can see declining fertility .
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7. Fertility rate
 Total fertility rate is the average no of children born to a
woman during her life
 This is better indicator of current fertility rates, but not effected
by the age distribution of the population (differ from CBR)
 Normally FR is higher in less economically developed
countries &lower in more economically developed countries.
 Common calculations related to fertility;
1 Total fertility rate(Average no. of children in a
“synthetic” family)
2 General fertility rate(No. of births per 1000 woman of
child bearing age)
3 Crude birth rate(No. of births/mid year population)
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8. Total fertility rate
 TFR is a synthetic rate but not based on the fertility of any
real group woman since this would involve waiting until
they had completed child bearing. But it is a reasonable
summery of current fertility levels.
 Related terms;
TFR - Total fertility rate
FR - Fertility rate
PTFR - Period total fertility rate
TPFR - Total period fertility rate
 TPFR is a better index of fertility than the CBR(Annual
no. of births per 1000 population) because it is
independent of the age structure of the population
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TFR of S/L

12. Replacement rates
 RR is the TFR at which new born girls would have an
average of exactly one daughter over their life times.
 If there were no mortality rate in the female population
until the end of the child bearing years of age (generally
44 or 49);then the replacement level of TFR would be
very close to 2.0 (but male births are slightly higher in
human population)
 Roughly, replacement fertility rate (RFR) of industrialized
countries is - 2.1 ; but due to higher mortality rate it is
about 2.5 to3.3 in developing countries
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13. Replacement level is affected by;
 Mortality
 Asexuality
 Genetic disorders inhibiting procreation
 Women who have no desire to have children
(Woman have just enough female babies to replace
themselves, or equivalently, adults have just enough
total babies to replace them selves)
 NRR - no. of daughters a woman would have in her
life time it is also important specially For the
areas male borns high
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14. When taken globally, the TFR at replacement is 2.33
children per woman
At this rate global population growth would trend towards
zero
If there is a high death or emigration rate and TFR also
not maintained more than regular values, population
dropped below replacement level, of it is carries forward
for several generations is called population lag effect.
In developed countries low FR,& MR(due to greater
wealth ,education and urbanization, birth control is
understood & easily accessible)
In developing countries the situation is observed
contravasary.
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15. Thank you
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