Measures of fertility

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

Dr Muhammad Tauseef Javed.

MEASURES OF FERTILITY

MEASURES OF FERTILITY

Population as a System

In-migrants

TotalPopulation

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

05/02/2023 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)


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


ImportanceFertility 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 processProduce 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)


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 FERTILITYUses:


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

BP

× 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.

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Birth Rate (births per 1,000 population)

Afghanistan 42Bangladesh 29Bhutan 37Brunei 25Burma 29Cambodia 42China 16Hong Kong 13India 26Indonesia 23Sri Lanka 18Taiwan 15Thailand 17Vietnam 22

Iran 31Japan 10Laos 41Macau 13Malaysia 27Maldives 40Mongolia 24Nepal 36North Korea 17Pakistan 34Philippines 28Singapore 14South Korea 16

CRUDE BR - ASIA

CRUDE BR - EUROPEBirth rate (births per 1,000 population)

Albania 21Austria 10Belgium 10Bosnia 9Croatia10Denmark 12Finland11France 12Germany 9Greece 10Hungary 11Iceland 15Ireland 13Italy 9

Luxembourg 11Netherlands 12Norway 13Poland 10Portugal 11Russia 28Serbia 13Spain 10Sweden 12Switzerland 11Ukraine 10UK 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.


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

ASBR Births Women Age Groups

49.9/1000 246 4928 15 - 19

201/1000 621 3088 20 - 24

269.9/1000 679 2516 25 - 29

263.8/1000 511 1937 30 - 34

191.3/1000 350 1830 35 - 39

103.1/1000 114 1106 40 - 44

67.7/1000 54 798 45 - 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=

6213088

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 51000

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

MeaningThe 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 fertilityDefined 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 = BWm

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…40In 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 51000

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 .

5Bf 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

5Bf x

GRRfB

B TFR ,

fB

B

No. of female BirthsTotal No. of Births

=~=


ASFRsdaughters

Female births Women Age Groups

24.6/1000 121 4928 15 - 19

98.1/1000 303 3088 20 - 24

131.6/1000 331 2516 25 - 29

128.5/1000 249 1937 30 - 34

93.4/1000 171 1830 35 - 39

50.6/1000 56 1106 40 - 44

32.6/1000 26 798 45 - 49 48

= GRR(24.6 + 98.1 + 131.6 + 128.5 + 93.4 + 50.6 + 32.6) x 5

1000

27971000 = 2.797=

49

Country Gross reproduction rate

Net reproduction rate Mean age of child bearing

Saudi Arabia 2.13 2.26 30.46Yemen 3.09 2.59 34.16Palestine 2.99 2.84 31.78Iraq 2.60 2.10 32.40Bahrain 1.7 1.7 31.20Emirates 2.26 2.22 30.46Oman 3.05 2.96 34.24Qatar 2.40 2.40 34.16Jordon 1.83 1.72 30.22Kuwait 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 womenNumber 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

f5Πx

f5Πx = survival rate =Mean size of the cohort of women of age x to x+5 Initial size of the cohort 05/02/2023 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.

ParityNumber 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. Calculate1. 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, and6. Net reproduction rate.


Age

Males Females BirthsSurvival

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


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Measures of fertility

Health & Medicine