Topic: Vital Statistics Measures of Fertility & Mortality, Specific Fertility Rates, Gross & Net Reproduction Rates.
Mortality: The number of deaths in a given time or place.
Mortality Rate: M.R is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of deaths per 1,000 individuals per year.
Measureś of Mortality Rate to Express Death Rates:
Broadly there are three types of death rates which can be used to know about depletion of population. They are:
(i) Crude death rate (C.D.R.)
(ii) Specific death rate (S.DR.)
(iii) Standardised death rate (S, D.R.)
i. Crude Death Rate (C.D.R.):
The Crude death rates are the simplest type of death rates. This is defined as the ratio of the number of deaths occurred in a specified period to the population under reference in the same period multiplied by 1000. a practice, the period is usually one year. So the formula can be given as,
No. of deaths in the year
C.D.R.= ------------------------------------------------- x 1000
Annual mean population
C.D.R., if not expressed as per thousand person but as simple ratio, it is equivalent to the probability of death of a person during the year under consideration.
The death rate so calculated is crude in the sense that it gives equal weightage to all age group persons which is not true.
➤ specific death rates are better than the crude death rates:
The experience tells that the deaths are not uniformly distributed in all sections of the population. They do differ in different age groups or according to sex, occupation or social status. Hence, it becomes necessary to know the mortality rates for various age groups or in women of child bearing age, etc. As an instance, we know that infant deaths are more than deaths in adolescence.
The child welfare societies will be interested in knowing mortality rates in children of 1 to 10 years
age. A women welfare organisation would be interested to know the death rate of women in the reproductive age group of 15 to 45 years and so on. Hence, specific death rates reveal categorically more than that what crude death rates do.
➤ Specific death rate for a specific section of the population:
The death rate for a particular segment of the population is known as specific death rate. It can, in
general, be calculated by the formula,
No. of deaths in the specified section of
a population in a given period
S.D.R.= --------------------------------------------------------------- x 1000
Average total population of the
specified section in the same period
Ds
---------------------x 1000
Ps
ii.Age Specific Death Rates:
The death rates calculated for the population consisting of the specified age group is called age
specific death rate (age-S.D R). Let the number of deaths in the age group x to (x + n) in a given period = nDx
nDx
Age S D.R.= ----------------------------- x 1000
nPx
(i) If x > 0 and (r + n) < 1 year, then, the Age S.D.R. is known as infant mortality rate. Thus, infant mortality is the number of child deaths under one year of age per 1000 live births.
(ii) The age- S.D.R. of the children under one month of age are called neo-natal mortality rate.
(iii) The death rate due to child birth among the women of child bearing age, i.e., 15-49 years
during a given year in a region is known as maternal mortality rate.
(iv) If the death rates are calculated for male and female populations Separately, they represent
the specific death rates
(v) Age specific death rate per thousand males can he calculated by a similar formula as above for male population only in the age group x to x + n as,
m
nDx Age-S.D. R = ---------------------------------- x 1000
m
nPx
Similarly for females:
f
nDx Age-S.D. R = ---------------------------------- x 1000
f
nPx
The main drawback of age specific death rates is that they are not capable to throw light on
mortality conditions prevailing in two different regions.
iii. standardised death rates:
We know that many social-economic factors do effect the death rates. Hence, to compare the death rates of two regions or communities, heterogeneity factors such as educational level, income, occupation, etc., be removed.In this way, the population is standardised. If the death rates are calculated by pooling death rates of different categories of populations of a region, they are known as standardised death rates.
Crude Birth Rate: Crude birth rate (C.B.R.) is the ratio of the number of live-births during the year to the total mean population during the same year.To express it per thousand persons, this ratio is nultiplied by 1000. As a formula,
Total No. of live - births during a year
C.B.R.= ----------------------------------------------------------------------- x 1000
Total mean population during the same year
Crude birth rate is hardly able to reveal any exhumating facts about fertility. Hence, one has to
resort to some specific fertility rates.
Fertility: Fertility is the average number of children born to a given generation of women throughout their fertile lives; their mortality is not taken into account. It is the sum of fertility rates by age in a generation.
Fertility Rate:The fertility rate at a given age (or for an age bracket) is the number of live children born to women of the age in question in the course of the year, as a proportion of the average population of women of the same age over the year in question.
By extension, the fertility rate is the ratio between the number of live births in a year and the whole female population of childbearing age (average number of women between 15 and 50 years of age over the year). Unlike total period fertility, the fertility rate is partly dependent on trends in the age structure of women between the ages of 15 and 50.
Measures of Fertility Rates:There are different types of fertility rates. Normally, six types of fertility rates have
been defined.
i General fertility rate (G.FR
ii Age specific fertility rate (A.S.FR.).
iii General marital fertility rate (G.M.FR.)
iv Age specific maritał fertility rate (A.S.M.FR.).
v Total marital fertility rate (T.M.FR.).
vi Total fertility rate (T.FR.).
i. General fertility rate: General fertility rate gives the rate of births per thousand women of child bearing age of a country or region in a given year without giving any cognizance to any other factor. In india, the child bearing age is 15-49 years. G.F.R. is obtained as the annual number of births divided by the mid-year population of women of child bearing age. In the formulaic form,
Annual number of births
G.F.R.= -------------------------------------------------------------------x 1000
Mid-year population of women
of age 15-49 of the region in the given year
General fertility rates do not provide adequate basis for effective planning with regard to reducing the
population growth and family welfare schemes.
ii. Age-Specific Fertility Rates is better than general fertility rate, and how can be calculated:
Population explosion is the most horrifying problem today before the world. Hence, to bring
down the population growth, one has to study it very minutely. We know that the fertility of women is not the same for all age groups.Hence, it seems germane to find ot the the marital status and age-specific fertility rates.
Age-specific fertility rate may be defined the as, th e number of births during a given period
(usually a calender year) to women of a specified age or age group divided by the average number of women of that age or age group living during that period (usually by the mid-year).
In the formulaic form,
No. of live births to the women of age group x to (x+n) during a year
A.S.F.R.= -----------------------------------------------------------------------------------------------------
Average No. of women in the same age group during that year
iii. General Marital Fertility Rates:
The births are continued to married women only barring exceptions of births to unmarried or
widow women. Hence, for family planning, emphasis has to be laid to married women only. For this it looks very logical to study the fertility rates among married women only.
General marital fertility rate can be defined as the number of offsprings born alive during a period (usually a year) per thousand married women of child bearing age. It can be formulated as,
No. of births during a year to married women
G.M.F.R.= ---------------------------------------------------------------------------- x 1000
Mid-year popułation of married women
during that year of age 15-49 years
G.M.FR. do not provide classified fertility rates of married women, particularly, in respect of age.
Hence, the information through G.M.FR. is not complete.
iv. Age Specific Marital Fertility Rates:
(More helpful in family planning programmes)
It is a known fact that fecundity varies with age. For example, in Indian women fecundity is
maximum in the age group 25-29 and is little less in the age group 20-24 also after 29 year of age it goes down. Hence, for the success of family planning schemes, it becomes necessary to study age-specific marital fertility rates.
A.S.M.F.R. is defined as, the number of children born alive during a given period (usually a calender year) per thousand married women of a particular age or age group. As a formula,
No. of live births to married women
during a year in the age group x to(x+n)
A.S.M.F.R. = --------------------------------------------------------------------------- x 1000
Mid-year population of married Women
during that year in the same group
v. Total Marital Fertility Rate:
Total marital fertility rate gives the total number of live births that would have taken place
per thousand married women, had the current schedule of age-specific marital fertility rates been applicable for the entire child bearing period. For the age group x to (x + n) years, the total marital fertility rate,
T.M.F.R. = A.S.M.R.R. x n
where n is the interval in years.
vi. Total Fertility Rate:
Total fertility rate is a measure which gives approximately the magnitude of 'complete family
size' that is the total number of children, a women would bear on an average in the lifetime assuming
no mortality and no adoption of family płanning measures. In short, the sum of age-specific fertility
rates over all ages of the child bearing period.
Formula for total fertility rate in the age group x to (x+n) is,
T.FR.= Sum of A.S.F.R. x n
To obtain the total fertility rate per woman, the above value of T.F.R. has to be divided by 1000.
Gross Reproduction Rate:
Ans. Population growth is dependent on the number of female births who are actually the future
mothers. Hence, population growth is certainly a function of the fertility rates to restricted the female
births. According to the demographic book, published the United Nations in 1954, "The gross reproduction rate indicates the average number of daughters who would be borned to a group of girls begining life together in a population where none died before the upper limit of child bearing age and where the given set of fertility rates was operation."
(i) No female children die till they attain upper limit of child bearing age which is 49 years in India.
(ii) Female population remains stagnant in spite of migration.
(iii) The current fertility rates continue to hold during the entire period of child bearing age.
The above assumptions are not relevant in real life. Hence, gross reproduction rate does not depict
a true picture.
Formula for gross reproduction rate.
No. of female live births
G.R.R.= ------------------------------------------------ x Total fertility rate
Total number of live births
Also, the gross reproduction rate can be calculated by making use of the current age specific fertility rate, under the assumption of no mortality, by the formula,
No. of daughters expected to be
borned to 1000 newly borned girls
G.R.R.= -------------------------------------------------------------
1000
Net reproduction rate: Net reproduction rate can directly be calculated by the formula,
No. of female babies expected to be borned to 1000
newly born female on the basis of current fertility and mortality rates
N.R.R.= -------------------------------------------------------------------------------------------------------
1000
The values of net reproduction rate: The experience gives some ideas about the values of N.R.R. and their importance as, follows:
i. N.R.R. varies from 0 to 5.
ii. N.R.R. can not exceed G. R. R. as N.R.R. takes into account the mortality.
iii. N.RR. will be equal to G.R.R. if all the newly borned female children survive till their maximum child bearing age.
iv. If N.RR. = 1, the female population will exactly replace itself into new generation and
population remains Constant.
v. If N.RR. < 1, this will result into the reduction in the number of mothers and will thus cause reduction in population.
(vi) If N.RR. > 1, there will be a greater number of mothers in the next generation which will tend to increase the population.
Drawbacks of Net Reproduction Rate:
Beside many good qualities of N.R.R. over G.R.R., it is not devoid of drawbacks such as:
(i) N.R.R. are based on the constant rates of fertility and mortality over generation which is not true to the real life phenomenon.
(ii) N.R.R. do not take into account the number of emigrants or immigrants. Many times, the
number is so large that it affects the reproduction rate.
(iii) A.S.F.R'S are also not so constant as they are taken to be for the purpose of N.RR.
A. R Statistics
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