Wednesday, August 26, 2015

Measures of Fertility

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General Fertility Rate (GFR):
GFR is the yearly number of live births per 1000 women of reproductive age group (usually 15-44 or 15-49). The GFR is,
Advantages of GFR:
The GFR is easy to compute and requires no additional information about births.
i. As a measure of fertility, it is not adequate because the denominator which measures women at risk has been approximated only roughly. That is, it does not take  into account the distribution of women within the reproductive age group 15-49.
ii. All unmarried women are included in the denominator.

Age Specific Fertility Rate (ASFR):
The frequency of childbearing varies considerably from one age group to another within the reproductive age group. This variation can be measured by computing the ASFR.
The ASFR is the yearly number of live births per 1000 women in each of the 7 age groups (15-19) (20-24), (25-29), (30-34), (35-39), (40-44) and (45-49).
It is a valuable measure of the current childbearing performances of women. It is not directly influenced by the age or sex composition of the whole population.
Where, nfx is the ASFR of women aged x to x+n years.
nBx is the number of births to women aged x to x+n years during the calendar year.
nWx is the midyear population of women in the same age group.

Total Fertility Rate (TFR):
Where the data are grouped into intervals of n years.
TFR is the number of children a women would have from 15 to the age 49 if she were to bear children at the prevailing age-specific rates (or the average number of children a woman will have if she experiences a given set of ASFR throughout her lifetime).
It is derived from ASFR. TFR is obtained by summing over all the ASFRs for each year of the childbearing span.

Cohort Fertility Rate (CFR):
CFR is the average number of children born per woman in a cohort by the end of their reproductive career. The term is also known as cohort completed fertility rate or completed family size. The formula is,
That is, by summing up the ASFR at each of all the 7 age intervals of the cohort whose members have completed their reproductive career multiplied by 5 and divided by the product 1000. 

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