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Unformatted text preview: SOCI 121: Population Problems F ERTILITY M EASURES Objectives: Discuss Fertility Measures Class Notes: Measuring Fertility The measures of fertility used by demographers attempt generally to gauge the rate at which women of reproductive age are bearing live children. o Most rates are based on period data, which refer to a particular calendar year and represent a cross section of the population at one specific time. o Cohort measures of fertility, follow the reproductive behavior of specific birth-year groups (cohorts) of women as they proceed through the childbearing years. Some calculations are based on a synthetic cohort that treats period data as though they referred to a cohort. Period Measures of Fertility o A number of period measures of fertility are commonly used in population studies, including the crude death rate, the general fertility rate, the child-woman ratio, the age-specific fertility rate, the gross reproductive rate, and the net reproductive rate. Each one tells a little different story because each is based on a slightly different set of data. o The Crude Birth Rate (CBR) is the number of live births ( b ) in a year divided by the total midyear population ( p ). It is usually multiplied by 1,000 to reduce the number of decimals: CBR = 000 , 1 p b The CBR is crude because: (1) it does not take into account which people in the population were actually at risk of having the births. (2) it ignores the age structure of the population, which can greatly affect how many live births can be expected in a given year. The CBR (which is sometimes simply called the birth rate) can mask significant differences in actual reproductive behavior between two populations. It can also imply differences that do not really exist. o For example, if a population of 1,000 people contained 300 women who were of childbearing age and 10 percent of them (30) had a baby in a particular year, the CBR would be (30 births/1,000 total people) = 30 births per 1,000 population. 1 SOCI 121: Population Problems However, in another population, 10 percent of all women may also have had a child in that year. Yet, if out of 1,000 people there were only 150 women of childbearing age, then only 15 babies would be born, and the CBR would be 15 per 1,000. Despite its shortcomings, the CBR is often used because it requires only two pieces of information: the number of births in a year and the total population size. o If, in addition, data on the distribution of the population by age and sex is available, then more sophisticated rates can be calculated....
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This note was uploaded on 11/02/2008 for the course SOCI 121 taught by Professor Lazar during the Fall '07 term at UNC.
- Fall '07