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Measures of Population Dynamics 2 Fertility

Measures of Population Dynamics 2 Fertility. Dr. J. Kivelia UDSM. Outline. Concept of Fertility Determinants of Fertility Measures of Fertility. Concept. Reproductive performance of a community Child bearing performance of women in a specified community

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Measures of Population Dynamics 2 Fertility

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  1. Measures of Population Dynamics 2Fertility Dr. J. Kivelia UDSM

  2. Outline • Concept of Fertility • Determinants of Fertility • Measures of Fertility

  3. Concept • Reproductive performance of a community • Child bearing performance of women in a specified community • Confined to women of child-bearing age, (i.e. 15 – 44 or 49 yrs) • Influenced by prevailing socio-economic and cultural contexts

  4. Determinants • Several, but main are FOUR • Marriage patterns • Levels of contraception • Infecundity • Abortion

  5. Fertility Measures • Fertility is measured from women point of view, using rates & ratios from child births. • Some of the major rates & ratios of fertility are: • Crude Birth Rate (CBR) • General fertility rate (GFR) • Child-Woman Ratio (CWR) • Age specific fertility rate (ASFR) • Total fertility rate (TFR) • Gross reproduction rate (GRR) • Net reproduction rate (NRR) • Calculation of these rates & ratios depend on data available.

  6. Crude birth rate • CBR is the number of births in a year per 1000 mid-year population. • The rate is normally expressed per 1000. • This measure is also called the birth rate • CBR is the simplest & commonest measure of fertility. • CBRs range from 10 in developed to 50 per 1000 in developing countries • CBR uses a formula:

  7. Age Specific Fertility Rate (ASFR) • ASFR is the number of live births occurring to women of a given age group. • ASFRs are normally expressed per 1,000 women or occasionally per woman. • It shows the relationship between births & age of mothers. • The formula for ASFR is:

  8. ASFR for TZ Mainland 1967 • The ASFR show low contribution of fertility to women in ages 15-19 & above 39 years • The peak is in women aged 20-24 followed by 25-29 • The ASFR pattern is common to developing countries

  9. ASFR for TZ Mainland 1967

  10. ASFR for Tanzania, 2002 Population Census

  11. Total Fertility Rate (TFR) • TFR is the total number of births a woman will bear in their lifetime • TFR represents the sum of ASFR over all ages of childbearing period in a single number. • TFR is among the fertility measures which are widely cited. • TFR gives the best picture of how many children a woman has. • The formula for computing TFR is: TFR = Sum of Age Specific Fertility Rates x 5 or TFR = 5Ʃfa Where fa is the ASFR of age group (a) • TFR ranges between 1 in developed countries & 8 in developing countries

  12. TFR by zone in Tanzania, 2008

  13. Global fertility levels

  14. Reproductive rates Gross Reproductive Rate (GRR) • GRR is the average number of daughters that would be born to a woman during her lifetime. • This rate is like the TFR except that it counts only daughters born. • GRR literally measures a woman reproducing herself by having a daughter. Net Reproductive Rate (NRR)  • NRR is the average number of daughters that would be born to a woman considering mortality • NRR is like the GRR, but it is always lower since it takes into account mortality of women. 

  15. GRR & NRR in DCs & LDCs • Table shows that during her life time: • a woman in Burkina Faso have 3.5 daughters • in UK a woman have less than one daughter. • In Burkina Faso, one daughter would die before completing her childbearing

  16. Replacement level fertility • Level at which women have exactly enough daughters to “replace” themselves in a population. • An NRR of 1.00 is equal to replacement level. • Today, virtually all developed countries are at or below replacement-level fertility. • UK, with an NRR of 0.85 in 1993, is below replacement. • TFR can be used to indicate replacement -level fertility. • This is through the average number of children sufficient to replace both parents. • A TFR of 2.1 is considered to be replacement-level.

  17. Exercise 4 • Citing examples, describe the influence of four main determinants of fertility on the current fertility level of Tanzania • Outline the main strengths and weaknesses of the following measures of fertility • CBR • CWR • ASFR • NRR • Use fertility data of the world to compare population growth of developing and developed countries

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