This article throws light upon the top ten methods used for measuring birth rate. The methods are: 1. Crude Birth Rate 2. Corrected Birth Rate 3. General Fertility Rate 4. Age Specific Fertility 5. Total Fertility Rate 6. Gross Reproduction Rate 7. Net Reproduction Rate 8. Completed Fertility Rate 9. Standardised Fertility Rate (SFR) 10. Cohort Fertility Rate (CFR).
Method # 1. Crude Birth Rate:
The number of births per thousand in a given year is called crude birth rate, which is related to the total population. In the words of Thomson and Lewis, “The crude birth rate for any specified population is obtained by dividing the number of births recorded in that population during a specified year by its total numbers, which gives a fraction of birth per person.”
B = Total live births during a given year
P – Total population at the middle of the same year.
In other words,
If the population of any area is 50,000 and the number of children born are 700 then,
It shows that the crude birth rate per 1000 population is 14.
Crude or natural birth rates are different in any country at different times, because crude birth rate is calculated after a particular month of the year. Moreover, the data for live births is based on the registered births, but all births are not registered generally.
Further, this measure of crude birth rate is not satisfactory because fertility is related to women and not to the whole population. Thus it is only a crude measure of fertility of a country.
Method # 2. Corrected Birth Rate:
Many a time in under-developed countries and especially in rural areas, corrected birth rate is sought, which is always greater than the crude birth rate. Corrected birth rate takes into account the registered births. The registration regarding birth in the rural area is not done properly by the concerned officials.
Often children die as soon as they are born. At that time, the registration regarding birth and death is essential, but it remains unnoticed. At times, when the assumed population is added to the crude birth rate, it is called corrected birth rate. Assume that in a population of 50,000 after 700 births, there occur 50 more births, then the corrected birth rate will be in the following way:
Thus the crude birth rate is 14 and the corrected birth rate is 15 per 1000 people which is greater.
Method # 3. General Fertility Rate:
The number of children born per year per thousand females in the age group of 15-49 years, is called the General Fertility Rate. In the words of Thomson and Lewis, “General Fertility Rate denotes the number of births per thousand women of child bearing age.”
It is calculated as follows:
B = Total live births during a given year.
PF= Number of females of age group 15-49 years.
In other words,
If the number of females of age group 15-49 years in an area is 5000 and the total of live births is 200 in a year, then
It indicates that there are 40 births per 1000 women in the child bearing age group.
Thomson and Lewis regard this measure better than the crude birth rate on two counts: First, it eliminates the influence of differences between males and females in the total population; and second, it eliminates differences in the proportion of women in 15-49 age group.
But this measure of birth rate has also certain weaknesses. The general fertility rate ignores the different child-bearing ages of women. In fact, the fecundity of women is low in the age group 15-19 years, high in the age group 20-29 when they are married and then starts declining till they reach 45 or 49.
Moreover, all women do not give birth to a child. In a country like India, some are widows and a few barren. Many prefer to remain unmarried or do not want to have a child in developed countries. According to Thomson and Lewis, the general fertility rate is usually four to five times high where the number of women in the child-bearing age is more. For the above reasons, this is not a true measure of birth rate.
Method # 4. Age Specific Fertility:
Age specific fertility rate is another refinement of birth rate. When the number of live births to women of definite age group per year is divided by the total number of females of that age group only and multiplied by 1000, we get the age specific fertility rate. It can be shown in formula as
Bf = Number of live births to women of a specific age group
PF = Mid-year women population in the same age group
K = 1000
In other words,
If the number of live births to women in the age group 25-29 is = 200 and the number of women in this age group is — 1200
In computing the age specific fertility rate, the age group of 5 years interval is taken. This measure of fertility rate is considered better than other measures because
(i) it provides age specific fertility rates for different age groups;
(ii) it shows changes in the reproductive capacity of women in different age groups;
(iii) it helps in analysing the frequency distribution of births among women in age specific groups;
(iv) a few stages can be outlined in the reproductive capacity of different age groups of women;
(v) we can also calculate age specific fertility rate in relation to only married women which is called age specific marital fertility rate;
(vi) it is the basis of calculating the total fertility rate; and
(vii) it helps the state in formulating policy with regard to the female marriage age.
Method # 5. Total Fertility Rate:
The total fertility rate is the sum of age specific fertility rates of women in all age specific groups. The formula is
Sum of age specific fertility rate x Magnitude of the age group
It can be understood with the help of the following hypothetical table.
The total fertility rate is a hypothetical rate that indicates “the total number of children that would ever be born to a group of women, if the group passed through its reproductive span of life with these birth rates in each year of age.”
This rate is based on the assumption that women in the hypothetical age group would live till they reach the end of the reproductive period. It is a useful device for comparing the reproductive capacity of women in different age groups.
Method # 6. Gross Reproduction Rate:
The gross reproduction rate relates the fertility rate to female births only. It is defined as the number of girls which are expected to be born to 1000 females passing through their child bearing years.
The gross reproduction rate is calculated from the total fertility rate in the following manner:
If the number of live births in a year is 25 crore, out of this 12 crore are female births and the total fertility rate is 9.78, then
This measure of fertility is based on the following assumptions:
(a) the age specific birth rates are constant for a given year;
(b) no woman dies during the child bearing age; and
(c) all girls survive.
These are unrealistic assumptions which ignore the current mortality rates of both present mothers and potential mothers. The net reproduction rate tries to remove these defects.
Method # 7. Net Reproduction Rate:
The net reproduction rate takes into account the complete reproduction period. The net reproduction rate is a good method of measuring birth rate which is based on reality. For the net increase in population growth, generally we consider factors responsible for increase in birth rate and decrease in death rate, but many a time, it also happens that if the girl dies before attaining maternity, the population will not increase.
Similarly, if the death rate is higher than the birth rate, even then there will be no increase in population. To understand this, it is necessary to know the net reproduction rate.
The net reproduction rate is the rate at which the newly born girls replace their mothers. It can be expressed as
No. of females expected to be born to 1000 newly born girls
For example, if 1000 females give birth to 1 girl each and 1000 girls are born and if these girls live till fertility, the net reproduction rate becomes 1000/1000 = 1.
Now, if the number of girls comes to 1200, this rate will be 1200/1000 = 12.
Against this, if this number becomes 800, then the net reproduction rate will become 800/1000 = 0.8 which means that the fertility rate is decreasing in the country.
This measure of fertility is also defective because it assumes that both birth and death rates remain constant during a generation. This is unrealistic. In fact, both birth and death rates are liable to change. Therefore, Thomson and Lewis opine that “these rates should not be used in making a prognosis of probable future growth of population.”
Method # 8. Completed Fertility Rate:
Generally, 15-49 years are considered to be the age of female fertility. But many a time a girl below 15 years of age and a women of more than 49 years may give birth to a child. Thus completed fertility rate measures the total number of live births per 1000 women of child bearing age, including widows and unmarried women. Thus
Method # 9. Standardised Fertility Rate (SFR):
The standardised fertility rate measures the age specific birth rates of two populations of different areas in order to convert them into a common standard. To calculate SFR, the number of females in one million population in a specific year is multiplied by their age specific birth rates which are then added to calculate the total number of births in all age groups 15-49 years.
This number is then multiplied by 1000 and divided by 10, 00,000 (1 million) which gives the standard fertility rate.
Suppose we want to find out SFRs of two towns A and B. The total calculated number of births of A town are 26,500 and of town B are 24,100, their standard fertility rates as per the following formula are
SFR reveals that the fertility in town A is 9.96% higher than in town B.
Method # 10. Cohort Fertility Rate (CFR):
The cohort fertility rate measures the average number of children who would be born to a cohort of women during their child bearing years 15-49 in a given year. To find CFR, the number of births occurring to women in each age group in the cohort are required.
This is calculated in the same manner as the age specific birth rate. If/ƒ(n) is the ability of a woman of a given cohort to give birth at age n, then the average number of births for that cohort is
where Σ (sigma) denotes the summing of age specific birth rates for ages 15 through 49. If CFR = 4.5, it means that women of that cohort would have an average of 4.5 births, had they lived through the age of 49 years.
As in the case of age specific fertility rate, this measure also assumes that the cohort of women does not experience any mortality and females of ages below 15 years and above 49 years do not give births.