Statistics>> Measurement of population growth
While calculating fertility rates, the sexes of the newly born babies are not taken care of. But the population growth depends mainly on the birth of female children who are the future mothers. Hence, population growth is mainly a function of fertility rate, restricted to female children, Reproduction rates are of two types.
1. Gross Reproduction Rate (GRR)
GRR gives the number of daughters that would be born by women arriving at and passing through the child bearing period. This rate is based on the following assumptions.
(i) A newly born female children is not subject to mortality till she attain the highest reproductive age i.e., 49 years.
(ii) A newly born female is subject to the given fertility conditions throughout her highest child bearing age.
(iii) There is no gain or loss due to migration.
GRR is calculated by summing annual female ASFR
WherefBx= No. of live births (female) to females in the age group (x, x + 1) in the given region during the given period.
GRR may be calculated from the formula
GRR = No of female births x TFR / Total Birth
If, for the child bearing age, the population of women and number of female children are given in 5-yearly age groups, then
GRR = 5 { f ix
One serious limitation of ORR is that it does not take into account the current mortality factor. All the female children born do not survive till they reach the child bearing age. For this ORR is called a hypothetical figure.
2. Net Reproduction Rate (NRR)
In computing the ORR we observed that mortality was not taken into consideration. The ORR is computed on the assumption that all newly born females will live throughout the child bearing period. But it is possible that the newly born females die before attaining the age of child bearing or may not marry or become widows. So, the ORR is to be corrected. By taking the factor mortality we get another measure of population growth called NRR.
IffLxis the number of females at age x out of the original group of femalesfl0then
If NRR = 1, then it shows that current fertility and mortality rates are such that the population will have tendency to remain constant lf NRR > 1, then it may be said to show a tendency to increase. If NRR < 1 then it may be said to show a tendency to decrease in the population.
作为一个衡量replac NRRement of population is not much relied upon because it does not take the factor migration into account.
Example 6: You are given the following data.
Age group:15-19 20-24 25-29 30-34 35-39 40-44 45-49
Female Population: 34 3"6 40 30 24 20 16
(in '000)
No. of live births:680 3,960 5,800 3,000 1,680 800 80 The total population in the city in 1991 was 7,00,000. Calculate Crude Birth Rate.
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