Measuring Fertility

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Measuring Fertility

• Two types of measures
• Period measures
• Cohort measures
• Cohort - a group who experiences a demographic
  event at the same time
• Birth cohort marriage cohort graduating class
  etc.
• Period - a combination of cohorts in a given year
  or other period.
• A snapshot of all cohorts at one point in time.

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Fertility

• The principle Period measures are
• The Crude Birth Rate (CBR)
• The General Fertility Rate GFR)
• The Child Woman Ratio (CWR)
• Coales Index of Fertility (Coales Index If)
• The Age-Specific Fertility Rate (ASFR)

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Fertility

• The Cohort Measures
• The Total Fertility Rate (TFR)
• The Gross Reproduction Rate (GRR)
• The Net Reproduction Rate NRR)

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Crude Birth Rate (CBR)

• Doesnt take into account
• age structure
• gender balance
• marriage rates
• Uses vital statistics (births) and census data
  (population)

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Crude Birth Rates
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General Fertility Rate (GFR)

• The fertility rate.
• 15-44 considered the children bearing years.
• Tends to be about 4.5 times CBR.
• Requires vital statistics and census data.
• An improvement over CBR, but more detailed data
  required.

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Child Women Ratio (CWR)

• Extends age range in denominator to account for
  the fact that some kids are now 4 (possibly born
  when mother was 45).
• Range About 200 to over 1000.
• Approx. 4.5 times GFR.
• 1990 279 in the US, 489 in Mexico.
• Advantage Census data only.

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Measuring Fertility

• Compute for each age group, x to x5.
• So we have a set or schedule of age specific
  rates.
• Requires age and sex information but controls
  for the age-sex structure of a population.

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Total Fertility Rate (TFR)

• Multiplied by 5 only if 5-year age intervals.
• 2 for 2-year intervals , and so on.
• Occasionally expressed per 1000.
• Most often applied as period measure to create a
  synthetic cohort.

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Gross Reproduction Rate (GRR)

• Number of female children a women may expect to
  have in her lifetime if her fertility follows
  current fertility rates and she survives through
  childbearing years.

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Low TFR Countries
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High TFR Countries
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Net Reproduction Rate (NRR)

• Like the GRR, but takes into account the
  mortality rates of women.
• Slightly smaller than GRR.
• Value of 1 indicates that the population will
  eventually quit growing or shrinking.
• Less than 1, population will shrink.
• Greater than 1, it will grow.

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The Coale (Princeton) Fertility Index (If)

• Births are compared to fertility of the Hutterite
  population
• B is the number of births in a given year
• wi is the number of women in the population at
  age i
• fi is the age specific fertility rate of
  Hutterite woment at age i
• Need births in a given year and age distribution
  of women

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Cohort Measures of Fertility

• Children Ever Born
• How many children born alive by the end of a
  cohorts childbearing years?
• Average for cohort often reported.
• Retrospective surveys often used to elicit
  thisexpensive and cant get the data until the
  childbearing years are over.
• Fertility Intention Surveys