crude birth rate, specific fertlity rate, total fertlity rate measures of fertlity

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Measures of fertility Crude Birth Rate  General Fertility Specific Fertility Rate  Total Fertility Rate .

Vital Statistics

Fertility. In demography, the word fertility is used in relation to the actual production of children or ‘occurence of births, specially live births’. Fertility must be distinguished from fecundity which refers to the capacity to bear children. In fact, fecundity provides an upper bound for fertility. As a measure of the rate of growth of population various fertility rates are computed.

 

In the following sections we shall discuss briefly some of the important rates which are usually computed to have an idea about the fertility in the relevant section of the population.

 

 Crude Birth Rate (C.B.R.) This is the simplest of all the measures of fertility and consists in relating the number of live births to the total population. This provides an index of the relative speed at which additions are being made through child birth.The fertility pattern of the above mentioned measure is given by crude birth rate (C.B.R.) defined as follows

$$\text{C.B.R. } = \frac{^Bt}{^Pt} \times 1000 $$

 

Bt =Total number of live births in the given region or locality

during a_given region.

Pt =Total population of the given region during the period t.

k= constant, usually 1000

Merits. It is simple, easy to calculate and readily comprehensible. It is based only on the number of births (B ) and the total size of the population (P) and does not necessitate the knowledge of these figures for different sections of the community or the population.

 

Demerits.  The crude birth rate, though simple, is only a crude measure of fertility and is unreliable since it completely ignores the age and sex distribution of the population.

 

2. C.B.R. is not a probability ratio, since the whole population I" cannot be regarded as exposed to the risk of producing children. In fact, only the females and only those between the child bearing age group (usually 15 to 49 years) are exposed to risk and as such whole of the male population and the female population outside the 'child-bearing age should be excluded from P  Moreover, even among the females who are exposed to risk, the risk varies from one  age group to another, a woman under 30 is certainly under greater risk as compared to a woman over 40.

 

3. As a consequence of variation of 'climatic conditions in Various countries, the child-bearing age-groups are not identical in all the countries. In tropical countries,;the period starts at an apparent earlier date. than in countries with cold wheather. Accordingly crude birth rate -does not enable us to compare the fertility situations in different countries.

 

4. Crude birth rate assumes that women in all the ages have the same fertility; an assumption which is not true since younger  women  have, in general higher fertility than elderly women. C.B.R. thus gives as :n estimate of a hetrogeneous figure and is unsuitable for comparative 'studies.

 

5. The level of crude birth rate is determined by a number of factors such as age and sex distribution-of the population, fertility of the population, sex ratio, marriage rate, migration, family planning measures and so on. Thus a relatively high crude birth rate may be observed in a population with a favourable age and sex structure even though fertility is low, a population with large proportion of the individuals in the age-group 15-49 years will have a high crude birth rate, other things remaining same.

 

Remarks . C.B.R. usually lies between 10 and 55  per thousand.

 

2. Since it is only a live birth that augments the existing popula tion, only live births are considered in measuring fertility, thus excluding  Still births.

 

 General Fertility Rate (G.F.R.) This consists in relating the total number of live births to the number of females in the reproductive or 'child bearing ages and is given by the formula

$$G.F.R. = \frac{^t B} {{\sum_{\lambda_{1}}^{\lambda_{2}}}^f P_x}\times K$$

 

 Bt=number of live births occuring among the population of a given geographic area during a given period t, 

$$ \displaystyle P_{x}^{f}$$={female population in the reproductive age in the given geographical region during the same time t}

          $$\displaystyle {{\lambda }_{{1,}}}{{\lambda }_{{2,}}}$$={lower and upper limits of the female child bearing age, and k=constant, usually 1000}

Thus general fertility rate may be defined as the number of babies ‘per k women in the reproductive age group.

 Remark. Generally$$\displaystyle {{\lambda }_{{1,}}}{{\lambda }_{{2,}}}$$                  are taken as 15 and 49. Thus births to “ females outside this range (i.e., below 15 and over 49) are very rare. Such births, if any are recorded separately and are included in the age group 15 and 49 respectively. 

Merits. 1. General fertility rate is a probability rate.

 

2, G.F.R. reflects the extent to which the female population in the reproductive ages increases the existing population through live births, Obviously, G.F.R. takes Into account the sex distribution of the population and also the age structure to a certain extent.

 

Demerits. G.F.R. gives a hetrogeneous figure since it overlook the age compositon of the  female poputauon  in the child-bearing age.Hence it suffers from the drawback of  non -comparability in  respect of time and country. 

 Specific Fertility Rate (S.E.R.) The Concept of specific fertility rate originated from the fact that fertllity is affected by  a number of factors such as age, marriage, migration, state' or region, etc.The fertility rate computed  with respect to any specific factor is called specific fertility rate and is defined as;

$$ \displaystyle S.F.R=\frac{{\mathbf{Number}\text{ }\mathbf{of}\text{ }\mathbf{births}\text{ }\mathbf{to}\text{ }\mathbf{the}\text{ }\mathbf{female}\text{ }\mathbf{population}\text{ }\mathbf{of}\text{ }\mathbf{the}\text{ }\mathbf{specified}\text{ }\mathbf{section}\text{ }\mathbf{in}\text{ }\mathbf{a}\text{ }\mathbf{given}\text{ }\mathbf{period}}}{{\mathbf{Total}\text{ }\mathbf{number}\text{ }\mathbf{of}\text{ }\mathbf{female}\text{ }\mathbf{population}\text{ }\mathbf{in}\text{ }\mathbf{the}\text{ }\mathbf{specified}\text{ }\mathbf{section}}}\times k$$

Where k=-1000, usually.

Age-specific Fertility Rate. In order to overcome the drawback of G.F.R. and get a better idea of the fertility  situation prevailing in  a community or locality it is necessary to compute the fertility rates for  different age-groups of reproducutive age separately. The fertility rate so  computed on the basis of specification w.r.t. age is  called the age-specific fertility rate. For its computation, 'the reproductive span is split into different subgroups and S.F.R. is worked out for each subgroup.

 Symbolicallay  the age-specific fertility rate for the age group x to x+n  is given by the formula ;

$$\displaystyle {}_{n}{{i}_{x}}=\frac{{{}_{n}{{B}_{x}}}}{{{}_{n}{}^{f}{{P}_{x}}}}\times K$$ 

$$\displaystyle {}_{n}{{i}_{x}}$$  =age specific fertility rate for age group for xto x+n

$$\displaystyle {}_{n}{{B}_{x}}$$  =number of  births to the female in age group xto x+n

x≤age<x+n

Remark; Age-specific fertility rete is a probability rate. It removes the ' drawback of G.F.R. by taking into account the age-composition of the women in the child-bearing age group and is thus suitable for comparative studies. However, the use of age-S.F.R. for comparing the fertility situations of two regions (or of the same region for two different periods) is not an easy job. Generally age-S.F.R. will be higher for certain age groups and lower for the remaining age-groups in one region than in the other. Accordingly it is diffcult to say if the fertility is higher or low in one region as compared to other.

 Total Fertility Rate (T.F.R.). As already pointed out that age-speciiic fertility rate is not of much practical utility for comparative purposes. In order to arrive at more practical measure of the population growth, the age specific fertility rates for different groups have to be combined together to give a single quantity.

   The average number of children that each woman would have if she lived to the end of her reproductive years and gave birth in accordance with the current age-specific fertility rate is known as the total fertility rate (TFR).

A simple technique is to obtain standardised fertility rate. This leads to total fertility rate (T.F.R.) which is obtained on adding the annual age specific fertility rates. Thus symbolically

$$T.F.R=\sum\limits_{{\lambda1}}^{{\lambda 2}}{{{{i}_{x}}}}=\sum\limits_{{\lambda 1}}^{{\lambda 2}}{{\frac{{{{B}_{x}}}}{{{}^{f}{{P}_{x}}}}}}\times K$$

Thus T.F.R. for a particular region during a given period may be regarded as an index of the overall fertility conditions operating in that region’ during the same period.

$$ \displaystyle {{\lambda }_{1}}=15,{{\lambda }_{2}}=49$$ 

also$$ \displaystyle T.F.R=\sum\limits_{x}{{n({}_{n}{{i}_{x}})}}$$

where summation is taken over different age-groups in the reproductive period.

Remarks 1. T.F.R. is a hypothetical figure giving the number of children born to a cohort of k= 1000 females (all born at the same time)

(1') 'none of them dies before reaching the end of the child bearing age, i.e, all of them live till at least the age of 50' years,-.and

 (ii) at each age-group ( in the child bearing ages) they are subject to the'fertility condition given by the observed age-speciiic fertility rate.

example;;Here's a table of some countries and their estimated total fertility rates in 2024:

Country	Total fertility rate (TFR)
Niger	6.73
Mali	5.91
Chad	5.76
South Sudan	5.53
Central African Republic	5.46
Uganda	5.37
Somalia	5.25
Burundi	5.25
Afghanistan	5.23
Mozambique	5.14

 

• TFR has declined globally in recent decades. This decline is attributed to factors such as increased education for women, improved access to contraception, and urbanization.  
• The lowest TFRs are found in East Asia and Europe. South Korea has the lowest TFR globally at 0.72, followed by Singapore at 0.82.
• The highest TFRs are found in sub-Saharan Africa. Niger has the highest TFR at 6.73.  
• TFR is a valuable indicator of population dynamics. It can be used to predict future population trends, assess the impact of population policies, and inform development planning.