Measures of fertility

MBBS.USMLE, DPH, Dip-Card, M.Phil, FCPS
Assct: Professor Community Medicine
Services Institute Of Medical Sciences Lahore.
Ex-Asst Professor Community Medicine
UmulQurrah University Makka Saudi Arabia

Population as a System
In-migrants
Total
Population
Population Gain
Population Loss
+
_
+
_ Migrational ChangeNatural Change
Births
Deaths Out-migrants

DEFINITION OF TERMS
 Fertility = Production of a live birth (natality)
 Infertility = Inability to produce a live birth
 Parity = Number of children born alive to a woman
 Gravidity = Number of pregnancies a woman has had whether or not they produce a live
birth
 Fecundity = Physiological capacity to conceive (reproductive potential)
 Infecundity (sterility) = Inability of a woman to conceive a pregnancy
- Primary sterility = Never able to conceive a pregnancy
- Secondary sterility= Inability to conceive after one or more children have been born
 Fecundability = Probability that a woman will conceive during a menstrual cycle
4/10/2017 4DR MUHAMMAD TAUSEEF JAVED SIMS

CONTENTS
 Introduction
 Uses of Fertility data
 Sources of Fertility data
 Measures of Fertility
 Crude Birth Rate (CBR)
 General Fertility Rate (GFR)
 General Marital fertility Rate (GMFR)
 Age Specific Fertility Rate (ASFR)
 Total Fertility Rate (TFR)
 Gross Reproduction Rate (GRR)
 Net Reproduction Rate (NRR) 4/10/2017 5DR MUHAMMAD TAUSEEF JAVED SIMS

LEARNING OBJECTIVE
You will be able to compute different indices of
fertility.
You will be able to spell out general
determinants of fertility.
You will be able to spell out usefulness of
fertility indicators.

FERTILITY MEASUREMENT: SOURCES OF DATA
 Censuses
 Vital registration systems
 Nationally representative sample surveys
 World Fertility Surveys (WFS),
 Demographic and Health Surveys (DHS),

CRUDE INDICATORS OF
FERTILITY

•Fecundity: The physiological capacity of women
to reproduce.
•Fertility:
In demography,
• it is the actual birth performance of a group of
women or to the relative frequency with which the
birth occurs in total population or in the population
exposed to it. This is the Result of fecundity
INTRODUCTION

Importance
Fertility behavior of a given time gives shape to the future age-sex
structure
Hence, studying the fertility behavior has an implication on the overall
welfare planning process
Produce the alterations in the size of a population
Sources of Data:
There are three sources:
 Registration of vital events
 PAKISTAN Demographic and Health Survey
 National family health surveys (NFHS) 4/10/2017 10DR MUHAMMAD TAUSEEF JAVED SIMS

Quantify the birth performance of a population over a period of
time.
Used to compare the fertility levels of a number of population,
during a particular time interval
Exhibit a time trend in fertility in a population in the study of
differential fertility by various socio-economic, racial and ethnic
groups.
MEASURES OF FERTILITY
Uses:

CHILD- WOMAN RATIO
 Number of children under age 5 per 1000 women of childbearing age in a given year. This
measure can be calculated from national censuses or survey data, thereby providing fertility
data where birth statistics may not otherwise be available.
CWR =

CRUDE BIRTH RATE (CBR)
 Ratio of the total number of live birth to the average
population ever lived during a given year and
geographical area.
 Where B = Total No. of live births in a given year & area.
P= Mid year population of the year
B
P
× 1000Crude Birth rate =

Factors affecting fertility
Population fertility (A factor affecting population change)
Measurements of fertility:
Crude birth rate is the common method of measuring fertility.
CBR = Total number of births X1000 or X100(%)
Total population
CBR does not take into account the age and gender (sex) of the population.
In 1997 this was 24 per 1000.

Birth Rate (births per 1,000 population)
Afghanistan 42
Bangladesh 29
Bhutan 37
Brunei 25
Burma 29
Cambodia 42
China 16
Hong Kong 13
India 26
Indonesia 23
Sri Lanka 18
Taiwan 15
Thailand 17
Vietnam 22
Iran 31
Japan 10
Laos 41
Macau 13
Malaysia 27
Maldives 40
Mongolia 24
Nepal 36
North Korea 17
Pakistan 34
Philippines 28
Singapore 14
South Korea 16
CRUDE BR - ASIA

CRUDE BR - EUROPE
Birth rate (births per 1,000 population)
Albania 21
Austria 10
Belgium 10
Bosnia 9
Croatia 10
Denmark 12
Finland 11
France 12
Germany 9
Greece 10
Hungary 11
Iceland 15
Ireland 13
Italy 9
Luxembourg 11
Netherlands 12
Norway 13
Poland 10
Portugal 11
Russia 28
Serbia 13
Spain 10
Sweden 12
Switzerland 11
Ukraine 10
UK 12

BIRTH / CRUDE BIRTH RATE
This is the number of live births per 1,000 population in a given year.
CBR =
Number of births X K
Total population
Example
If the number of births in a community in 2017 was 18,247 and the mid-year population size was 985,210.
What is the crude birth rate of this community?
Interpretation: There were ? births per 1,000 in community X in year 2017.
 Births are only one component of population change, and the birth rate should not be confused with the
growth rate, which includes all components of change.

DATA REQUIREMENT AND LIMITATIONS OF CBR
 Need a complete and accurate vital registration system.
 Only a crude estimate of fertility.
 All the population included in the denominator is not exposed to the risk of pregnancy.
 Not good for comparing fertility across populations, as variations in age distribution of the
populations being compared will affect the birth rate.

GENERAL FERTILITY RATE
 The general fertility rate (also called the fertility rate) is the number of live births per 1,000
women ages 15-49 in a given year.* The general fertility rate is a somewhat more refined
measure than the birth rate because it relates births to the age-sex group at risk of giving
birth (usually defined as women ages 15-49).
 This refinement helps eliminate distortions that might arise because of different age and sex
distributions among populations. Thus, the general fertility rate is a better basis to compare
fertility levels among populations than are changes in the crude birth rate.
GFR =

 Merits
 Requires minimum data on fertility
 Easy to interpret
 Demerits
 Cannot be used to compare the levels of fertility for any two
populations because they may differ widely in their age-sex
composition.
 It is not a fertility rate as it includes all the population either
exposed or not exposed to the risk of child bearing. 4/10/2017 20DR MUHAMMAD TAUSEEF JAVED SIMS

DATA SOURCES
 Vital registration system for births
 May also be estimated from national censuses or survey data using the child-women ratio
when birth statistics are not available
 Relates births to the age-sex group at risk of giving births (usually defined as women ages
15-49 years)
 More refined measure than crude birth rate to compare fertility across populations
 Approximately equals to 4 times the crude birth rate

AGE ADJUSTED INDICATORS OF
FERTILITY

Total fertility rate is the number of children born to a women
during her lifetime (Child bearing years is usually referred to as
15-49). Hence more accurate than Crude Birth rate.
TFR obviously varies across the world and currently the world TFR is
3.1. The TFR for the UK is 1.8 and in Sierra Leone (West Africa) it is
6.5.
Age specific fertility rate (ASFR) is a measure of the number of
children born to each age group, in relation to the number of
woman in that age group Seven age groups are conventionally used
across the span 15-49 years. ASFRs are normally expressed as per
1000 women in each age group.
More
definitions

AGE SPECIFIC FERTILITY RATE
 Number of births per 1000 women of a specific age (group) in a given year. Fertility rates is
calculated for specific age groups to see differences in fertility behavior at different ages or
for comparison over time.
ASFR =

Age Specific Fertility Rate (ASFR)
ASD = Live births for women at the
reproductive age X
Women at the reproductive
age x at mid-year
The below table shows the distribution of women
according to live birth during the past year,
Calculate the ASFR and the TFR
X 1000
25

ASBRBirthsWomenAge Groups
49.9/1000246492815 - 19
201/1000621308820 - 24
269.9/1000679251625 - 29
263.8/1000511193730 - 34
191.3/1000350183035 - 39
103.1/1000114110640 - 44
67.7/10005479845 - 49 26

For example, ASBR for the interval (20 – 24), can
be calculated as:
Live births to women aged 20-
24
Mid-year population for
Women aged 20-24
X 1000ASFR20-24 =
621
3088
X 1000 = 201/1000
27

AGE SPECIFIC FERTILITY RATES: WHY DO WE NEED THEM?
 For comparisons in fertility behavior at different ages
 For comparison of fertility at different ages over time
 For comparison of fertility across countries/populations

Uses:
 For comparisons in fertility behavior at different
ages
 For comparison of fertility at different ages over
time
 For comparison of fertility across
countries/populations
29

TOTAL FERTILITY RATES
 The average number of children that would be born to a woman by the time she ended
childbearing if she were to pass through all her childbearing years conforming to the age-
specific fertility rates of a given year.
TFR = 5 X ΣASFR / 1,000

Total Fertility Rate (TFR)
 Calculated from the set of age-specific fertility
rates.
 A major advantage of the TFR it produces a
single summary figure from seven age-specific
fertility rates.
 It measures “average family size”
31

Total fertility rate (TFR):
= TFR
Sum of ASFRs x 5
1000
Note that:
1- Each ASFR usually relates to 5 years. It can be
though of as the average of the rates for each of
the 5 years. It is necessary to multiply the
32

Five-year rate by 5.
2- The TFR is always expressed per woman, where
as ASFRs are often expressed per 1000. Then it is
necessary to divide by 1,000.
• Using the previous table, TFR is:
(49.9 + 201 + 269.9 + 263.8 + 191.3 + 103.1 + 67.7) x 5
1000
= 5.73 33

Meaning
The average number of children that would be
born to a woman by the time she ended
childbearing if she were to pass through all her
childbearing years and bear children in
accordance with current age-specific fertility
rates.
• In our example, the average number of children
or family size is 6
34

35
The number, which ranges from more than 7
children per woman in developing countries in
Africa to around 1 child per woman in Eastern
European and highly-developed Asian countries.
and bear children in accordance with current age-specific
fertility rates.

 TFR is a “synthetic” measure of fertility that is independent of
age structure of a population
 Best single measure to compare fertility across populations
 Does not give a measure of actual number of births any woman
will have all through her reproductive years

CHILDREN EVER BORN (CEB)
 This is computed from censuses or sample surveys by asking women their age and number
of live births they ever had (including those having died since birth)
 Provides one measure of population fertility
 Useful only if age group of women is considered
 Data can be used by demographers to indirectly estimate ASFR and TFR in a population.
 CEB for women over age 49 is called Completed Fertility Rate; it shows how many children
on average a certain cohort of women who have completed childbearing actually produced
during their childbearing years.

INDICATORS OF REPRODUCTION

GENERAL FERTILITY RATE (GFR)
Simplest measure of fertility
Defined as the number of births per year per thousand mid-
year woman of the child bearing ages.
W 15-49 = total number of women of child bearing age 15-49 at the
mid point of the year in a given geographical area.
GFR =
B
W 15-49
× 1000

GENERAL FERTILITY RATE (GFR)
 Is the number of live births per 1000 women in the reproductive age group (15-49 years) in a
specific year:
 GFR No of births
 Women in 15-49 age range X1000 per Year

Advantages:
 It includes the female population in their reproductive
ages who are supposed to be exposed to the risk of
giving birth.
 Generally used in population projection using
component projection method.

GENERAL MARITAL FERTILITY RATE (GMFR)
 Overall measure of fertility of married women.
 It is the number of births per year per thousand mid-
year married women within reproductive ages.
Symbolically,
Wm
15-49 = total no. of married women of child bearing age 15-49 at
the mid-point of the year
GMFR = B
Wm
15-49
× 1000

TOTAL MARITAL FERTILITY RATE (TMFR)
 An over all summary measure of marital fertility,
 Obtained by summing the age- specific marital fertility rate for each
age of the child bearing span.
for x= 15,20.25…40
In this case n=5
TMFR = 5 × ∑
x
5gx

Number of children which a women of hypothetical cohort
would bear during her life time if she were to bear children
through out her life at the age-specific fertility rates for given
year and if none of them dies before crossing the age of
reproduction.
for single year ASFR.
for 5year ASFR.
For x = 15, 20, 25.……
In this case n=5
Total Fertility Rate (TFR)
TFR = ∑fx
X
TFR = 5 × ∑ 5fx
X

Gross Reproduction Rate
 For TFR we considered population replacement in
terms of total children born.
 Proliferation of people is measured by number of
female births because they represent the generation
that bears the responsibility of reproduction in the
future.
45

The gross reproduction rate resembles the TFR,
except it measures the number of daughters per
woman, instead of the total number of children.
Calculation of GRR =
= GRR Sum of ASFRs for daughters x 5
1000
X1000
46

Indicates the number of daughters of a hypothetical cohort of women by
the end of the reproductive life if she bears the births according to a
given schedule of age-specific fertility rates( taking only female births)
without experiencing any mortality till the end of reproductive life .
5B
f
x = no. of female births to women aged x to x + 5.
Limitation of GRR: It dose not consider the mortality of the cohort of
women.
Gross Reproduction Rate (GRR):
Measure of population replacement
GRR= 5 ∑
x=15 5Wx
5B
f
x
GRR
fB
B
 TFR ,
fB
B
No. of female Births
Total No. of Births
=
~=

ASFRs
daughters
Female
births
WomenAge Groups
24.6/1000121492815 - 19
98.1/1000303308820 - 24
131.6/1000331251625 - 29
128.5/1000249193730 - 34
93.4/1000171183035 - 39
50.6/100056110640 - 44
32.6/10002679845 - 49 48

= GRR
(24.6 + 98.1 + 131.6 + 128.5 + 93.4 + 50.6 + 32.6) x 5
1000
2797
1000
= 2.797=
49

Country Gross reproduction
rate
Net reproduction rate Mean age of child
bearing
Saudi Arabia 2.13 2.26 30.46
Yemen 3.09 2.59 34.16
Palestine 2.99 2.84 31.78
Iraq 2.60 2.10 32.40
Bahrain 1.7 1.7 31.20
Emirates 2.26 2.22 30.46
Oman 3.05 2.96 34.24
Qatar 2.40 2.40 34.16
Jordon 1.83 1.72 30.22
Kuwait 2.38 2.35 29.95
50

Gross Reproduction Rate (GRR)
Average number of daughters that would be born to a woman during her lifetime if she
passed through her child-bearing years conforming to the age specific fertility rates of a
given year.
Note: GRR is exactly like TFR, except that it counts only daughters and literally measures
“reproduction”– a woman reproducing herself in the next generation by having a daughter.
 Let Bf = Number of female births
 Bm+f = Number of male and female births i.e. all births

GRR Cont’d
 GRR = TFR ∗ (Proportion of female births)
 GRR, Uganda ,1991: Sex ratio at birth = 1.03M/F

GRR Cont’d
 GRR, like TFR, assumes that the hypothetical cohort of women pass from birth through their
reproductive life without experiencing mortality.
 This assumption is satisfactory when one wants to compare levels of fertility and/or gross reproduction
across populations and over time.
 But, for a more realistic assessment of the reproductive potential of a population, taking into account
mortality, one needs to calculate the Net Reproduction Rate (NRR).

NET REPRODUCTION RATE (NRR)
Definition
 Average number of daughters that would be born to a woman if she passed through her life-time from
birth to the end of her reproductive years conforming to the age-specific fertility and mortality rates of
a given year

NET REPRODUCTION RATE: RELATIONSHIP WITH GRR AND TFR
 NRR is always lower than GRR, because it takes into account the fact that some women will die before
entering and completing their child-bearing years.
 Correspondingly NRR will be less than half the magnitude of the TFR.

NRR is GRR adjusted for mortality schedule of cohort of women
Number of daughter that would be born to a cohort of women
during their lifetime if they experience a fixed scheduled of ASFR
and ASMR , therefore,
Net Reproduction Rate (NRR):
NRR = 5
∑
x=15
nBx
×
5Wx
f
5Πx
f
5Πx = survival rate =
Mean size of the cohort of women of age x to x+5
Initial size of the cohort 4/10/2017 56DR MUHAMMAD TAUSEEF JAVED SIMS

( Continued……….)
Replacement Level Fertility:
 Women replace with their offspring
 This is the level of fertility that gives NRR=1.
 Generally takes the value, the total fertility rate of level 2.1 children per
women in a population.
 It is the precondition for population stabilization (process to achieve
zero growth of population)

REPLACEMENT FERTILITY
 Replacement Level Fertility is said to have been reached when NRR=1.0
– Surviving women in the hypothetical cohort have exactly enough daughters (on average) to replace themselves in
the population
 At this time GRR>1 and TFR>2. (Roughly, this is when couple have an average of two children.)
 When NRR=1.00 it does not imply:
– CBR= CDR
– Population growth rate = 0

Replacement level fertility –When there is just enough
children born to balance the numbers that die i.e. keep the
population totals constant. The figure is about 2.1(TFR). The
figure is over 2 due to child mortality rates/females dying during
the child bearing period and therefore some females do not go
through the full child bearing age and have less children and on
average there are slightly more boys than girls born. Example 100
females have 210 children and 10 die before they reach child
bearing age etc.
Task 8: Write down this
definition

RELATIONSHIP BETWEEN REPRODUCTION MEASURES AND
POPULATION GROWTH
 Population momentum is the propensity for a population to grow for many years after fertility declines
to reach the replacement level of the “two-child family”. (TFR ~2.2 and NRR=1.0).
 This population momentum during the fertility transition is a function of young age structure of the
population due to high levels of fertility in the past.

Children Surviving (CS)
Total number of children , which a women has born as live births and
they are still live.
Children Ever Born (CEB)
It is a cohort measure
It is the total number of children a women has born till the date. Also
include those children , which a women has born as live births but
they died at any time later.
Parity
Number of birth a women has given

Exercise:
The following table gives the population of a country for the year 1951, together
with the estimated numbers of births and deaths based on a special vital
statistics enquiry conducted in the country. Calculate
1. Crude death rate for the total population and for males and females.
2. Crude birth rate for the total population,
3. General fertility rate,
4. Total fertility rate,
5. Gross reproduction rate, and
6. Net reproduction rate.

Age
Males Females Births Survival
RatesPopulation Deaths Population Deaths Males Females
0 - 04 442532 18623 434980 17308
05 - 09 419042 1809 416736 1709
10 - 14 393543 984 384616 1638
15 -19 308269 1233 314056 1329 3578 3343 0.914
20 -24 257852 1289 269340 1481 7293 6690 0.899
25 - 29 230629 1776 236187 1677 6775 6361 0.844
30 - 34 204188 1633 203477 1465 4233 4187 0.868
35 - 39 182270 1588 176534 1289 2999 2685 0.852
40 - 44 162509 1967 145037 1233 593 725 0.834
45 - 49 128784 2138 122949 1352 129 128 0.819
50 - 54 102971 1905 96589 1188
55 - 59 80717 2478 78311 1605
60 - 64 58899 3099 58142 1980
65 - 69 37797 2428 39099 2468
70+ 45099 5981 48866 7175

THANK YOU

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