Measures of fertility

1. Measurement of Fertility
Dr Inn Kynn Khaing
M.B.,B.S, MPH, MSc (Healthcare Administration) (Japan)
Lecturer, Department of Biostatistics

2. 1. Crude Birth Rate (CBR)
 Ratio of the total number of registered live births among residents in
an area during a calendar year to the total mid-year estimated
population of the same area, also multiplied by 1,000.
 The number of births and death are supplied by vital registration
system
CBR =
B
P
x K
B = total number of live birth registered during the calendar year
P = total mid-year estimated population or the total population of the
middle of the year i.e. as on 1st July
K = a constant usually taken as 1,000

3. 1. Crude Birth Rate (CBR)
Advantages
 Simplest and commonest measure on fertility
 Easily calculated
Limitations
 The entire population is in the denominator, whereas all
members of the population do not contribute equally to births
 In spite of its limitation, it is widely used due to the availability
of data

4. 2. General Fertility Rate (GFR)
 GFR avoids some of deficiencies of CBR by changing
denominator from total population to number of women in
the reproductive age groups usually 15 to 49 years
 GFR is a ratio of total yearly registered live births to the
female population of “child bearing age” i.e. from 15 to 49
years
GFR =
No: of total registered live birth of residents in a
community in a year
Total female population aged 15 to 49
X 1,000

5. 2. General Fertility Rate (GFR)
 To restrict the denominator to potential mothers by excluding
all men and large group of women not “exposed to the risk” of
child bearing by reason of age
 A step in the direction of measuring fertility against the proper
proportion of the population
 Can be calculated as easily as the CBR and requires only the age
and sex distribution of the population
 Advantages : Can be computed in situation in which the
registration of the births and the enumeration of the
population are satisfactory but where direct evidence of births
by age of parents is lacking

6. 3. Age Specific Fertility (Birth) Ratio (ASFR)
 One of the most important determinants of the fertility of a
population is the age of the mother
 Refinement: overall fertility measure is obtained by
distinguishing the women of the child bearing age according
to their ages and similarly subdividing the births according to
the ages of the mothers
 Age means the age of each parent at the time of birth.
 ASFR : maternal birth rates than paternal birth rates

7. 3. Age Specific Fertility (Birth) Ratio (ASFR)
 defined as the number of births to one of a specific age group
per 1,000 women in that age group usually in 5 year age
intervals
 A set of rate for 5 year age group from 10-14 to 45-49/ 15-19
to 45-49 or 15-19 to 40-44.
fi =
Bi
Pi
x K
B = total number of live birth registered during
the year to women in the age interval i
P = mid-year female population in the same age
group
K = a constant usually taken as 1,000

8. 3. Age Specific Fertility (Birth) Ratio (ASFR)
Formula for ASFR at ages 20-24 is f20-24 =
B20-24
P20-24
x 1,000
Age group of
mothers (year)
Female
population
Live births ASFR
15-19 2306 154
20-24 1938 429
25-29 1661 382
30-34 1520 251
35-39 1306 199
40-44 1177 77
45-49 971 13
All ages total

9. 4. Total Fertility Rate (TFR)
 Sum of age specific fertility rates of women over their
reproductive span i.e. all ages of child-bearing period from 15
to 49 years of age as observed in a given year.
TFR = ∑
Bi
Pi
x 1,000
i = 49
i = 15
B = total number of live birth registered during the year to mothers of age i
where I is an interval of one year
P = mid-year female population in the same age group

10. 4. Total Fertility Rate (TFR)
 Usual practice, subscript i represents 5 year intervals such as
15-19, 20-24,…. And 45-49 years
TFR = 5 ∑
Bi
Pi
x 1,000
i = 7
i = 1
B = number of live birth registered during the year to mothers of age I
where I is an interval of 5-years
P = mid-year female population in the same age group

11. 5. Gross Reproduction Rate (GRR)
 A special case of TFR
 Only distinction: the numerator of GRR is based on female births
instead of total births
 TFR measures the total number of children a cohort of women will
have
 GRR measures the number of daughters it will have
 This rate is of considerable experience in demographic theory, as it
shows the extent to replace themselves, as far as the fertility level is
concerned
 GRR shows the average number of female children born to women
living through the child bearing ages (i.e. 15 to 49 years), assuming
no mortality

12. 5. Gross Reproduction Rate (GRR)
 Suppose GRR is 3. if a female child is born at that time, and
survives through her child-bearing period then she will give
birth to 3 female children in her turn, on the average
GRR = ∑
Bx
f
Px
f
x 1,000
w1
w2
Bx
f = number of female infants born to mothers of age x
Px
f = number of women of age x in the mid-year population
w1 and w2 = the lower and upper limits of the child bearing period
K = 1,000

13. 6. Net Reproduction Rate (NRR)
 This rate consists of a hypothetical cohort of women, their
deaths and their female births during their child-bearing
period i.e. 15 to 49 year
 NRR is a measure of the number of daughters that a cohort of
new born girl babies will bear during their life time assuming a
fixed schedule of fertility rates and a fixed set of mortality
rates
 NRR is a measure of the extent to which a cohort of newly
born girls will replace themselves under given schedule of age
specific female of fertility and mortality

14. 6. Net Reproduction Rate (NRR)
NRR = Bx
f
Px
f
x 1,000
fx = age specific female birth rate (daughters only) at age x
 NRR rate 1 means exact replacement
 NRR above unity indicates that the population is more than
replacing itself
 NRR below unity indicates that the population is not replacing itself
NRR is always lower than GRR because it takes into account that
some women die before completing their childbearing years.

15. 7. Child-women ratio
 Ratio of children under age 5 to women of ‘child bearing ages’
 Index – a makeshift designed to furnish a measurement of
fertility when birth statistics are lacking
 Derived entirely form the data by age in one census
 Serves best as a relative measure to compare the fertility
performance of different section of same population, where
the disturbing effects of these other factors are presumed to
be smaller
 Disturbing effect: instead of birth, the ratio is based on
survivors of previous births

16. 7. Child-women ratio
Child-
women =
ratio
No: of children under 5 or 0-4 years of age in a
population
No: of women of child bearing age i.e. 15-49
X 1,000

17. De-facto method of enumeration
 Counting of the people actually present at some moment in
those places, as of midnight on the census date.
 Conducted synchronously over the whole area
 Attempts to count all persons in the actual places where they
happened to be at the time of census
 If de-fato method of enumeration is carried out at different
times, there is a danger that a person who has travelled from
one place to another – may be counted twice or he may be
omitted from the count together

18. De-facto method of enumeration
 It requires a large staff to carry out a synchronous
enumeration
 This is justified in areas where the population is fairly dense
but not justified in areas where the population is thinly
distributed
 A much smaller staff is used to enumerate the population in
the thinly populated areas who travel over a wide area and
carry out the census at different times in different places
 In such case, de facto method cannot be used

19. De-jure method of enumeration
 Counting people usually or normally or permanently present
in some places
 Non synchronous method of enumeration may last two or
three months.
 Suitable for loosely administered and sparsely populated part
of the country
 A person is enumerated only in the place where he or she
normally resident even though he or she may not be there at
the time of the enumeration

20. De-jure method of enumeration
 It is assumed that every person has only one normal place of
residence
 It is attempted to reduce the errors of omission or double-
counting
 Some errors still remain because the census idea of normal
residence is not well understood and a person may be
reported as the normal resident of more than one place or
may be omitted altogether.