Total fertility rate

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Not to be confused with birth rate.
A world map showing countries by total fertility rate (TFR), according to the CIA World Factbook's 2015 data.
A world map showing countries by total fertility rate (TFR), according to World Population Prospects 2015 by UN.

The total fertility rate (TFR), sometimes also called the fertility rate, period total fertility rate (PTFR) or total period fertility rate (TPFR) of a population is the average number of children that would be born to a woman over her lifetime if:

  1. She were to experience the exact current age-specific fertility rates (ASFRs) through her lifetime, and
  2. She were to survive from birth through the end of her reproductive life.[1]

It is obtained by summing the single-year age-specific rates at a given time.

Parameter characteristics[edit]

Total fertility rate by region
Total fertility rate for selected countries
World historical TFR (1950–2015)
UN, average variant, 2010 rev.[2]
Years TFR
1950–1955 4.95
1955–1960 4.89
1960–1965 4.91
1965–1970 4.85
1970–1975 4.45
1975–1980 3.84
1980–1985 3.59
1985–1990 3.39
1990–1995 3.04
1995–2000 2.79
2000–2005 2.62
2005–2010 2.52
2010–2015 2.36

The TFR is a synthetic rate, not based on the fertility of any real group of women since this would involve waiting until they had completed childbearing. Nor is it based on counting up the total number of children actually born over their lifetime. Instead, the TFR is based on the age-specific fertility rates of women in their "child-bearing years", which in conventional international statistical usage is ages 15–44 or 15–49.[3]

The TFR is, therefore, a measure of the fertility of an imaginary woman who passes through her reproductive life subject to all the age-specific fertility rates for ages 15–49 that were recorded for a given population in a given year. The TFR represents the average number of children a woman would potentially have, were she to fast-forward through all her childbearing years in a single year, under all the age-specific fertility rates for that year. In other words, this rate is the number of children a woman would have if she was subject to prevailing fertility rates at all ages from a single given year, and survives throughout all her childbearing years.

Related parameters[edit]

Net reproduction rate[edit]

An alternative fertility measure is the net reproduction rate (NRR), which measures the number of daughters a woman would have in her lifetime if she were subject to prevailing age-specific fertility and mortality rates in the given year. When the NRR is exactly one, then each generation of women is exactly reproducing itself. The NRR is less widely used than the TFR, and the United Nations stopped reporting NRR data for member nations after 1998. But the NRR is particularly relevant where the number of male babies born is very high (see gender imbalance and sex selection). This is a significant factor in world population, due to the high level of gender imbalance in the very populous nations of China and India. The gross reproduction rate (GRR), is the same as the NRR, except that—like the TFR—it ignores life expectancy.

Total period fertility rate[edit]

The TFR (or TPFR—total period fertility rate) is a better index of fertility than the crude birth rate (annual number of births per thousand population) because it is independent of the age structure of the population, but it is a poorer estimate of actual completed family size than the total cohort fertility rate, which is obtained by summing the age-specific fertility rates that actually applied to each cohort as they aged through time. In particular, the TFR does not necessarily predict how many children young women now will eventually have, as their fertility rates in years to come may change from those of older women now. However, the TFR is a reasonable summary of current fertility levels.

Tempo effect[edit]

The TPFR (total period fertility rate) is affected by a tempo effect—if age of childbearing increases (and life cycle fertility in unchanged) then while the age of childbearing is increasing, TPFR will be lower (because the births are occurring later), and then the age of childbearing stops increasing, the TPFR will increase (due to the deferred births occurring in the later period) even though the life cycle fertility has been unchanged. In other words, the TPFR is a misleading measure of life cycle fertility when childbearing age is changing, due to this statistical artifact. This is a significant factor in some countries, such as the Czech Republic and Spain in the 1990s. Some measures seek to adjust for this timing effect to gain a better measure of life-cycle fertility.

Replacement rates [edit]

Replacement fertility is the total fertility rate at which women give birth to enough babies to sustain population levels.

If there were no mortality in the female population until the end of the childbearing years (generally taken as 44, 45, or 49, though some exceptions exist) then the replacement level of TFR would be very close to 2.0. The replacement fertility rate is roughly 2.0 births per woman for most industrialized countries (2.075 in the UK, for example), but ranges from 2.5 to 3.3 in developing countries because of higher mortality rates.[6] Taken globally, the total fertility rate at replacement is 2.33 children per woman. At this rate, global population growth would tend towards zero.

A log-transformation of the data gives an alternative view of the relation. The coefficients taken literally imply that for each 1% advance in GDP, TFR diminishes by 0.26%.

Same fig., after log transformation. Circles proportional to population

Population-lag effect[edit]

A population that maintained a TFR of 3.8 over an extended period without a correspondingly high death or emigration rate would increase rapidly (doubling period ~ 32 years), whereas a population that maintained a TFR of 2.0 over a long time would decrease, unless it had a large enough immigration. However, it may take several generations for a change in the total fertility rate to be reflected in birth rate, because the age distribution must reach equilibrium. For example, a population that has recently dropped below replacement-level fertility will continue to grow, because the recent high fertility produced large numbers of young couples who would now be in their childbearing years.

This phenomenon carries forward for several generations and is called population momentum, population inertia or population-lag effect. This time-lag effect is of great importance to the growth rates of human populations.

Symbol radius reflect population size in country

TFR (net) and long term population growth rate, g, are closely related. For a population structure in a steady state and with zero migration, g equals log(TFR/2)/Xm, where Xm is mean age for childbearing women and thus P(t) = P(0)*exp(g*t).- At the left side is shown the empirical relation between the two variables in a cross-section of countries with most recent y-y growth rate. The parameter 1/b should be an estimate of the Xm; here equal to 1/.02 = 50 years,- way off the mark because of population momentum. E.g. for log(TFR/2) = 0 g should be exactly zero, which is seen not to be the case.

Developed or developing countries[edit]

Further information: Income and fertility

Developed countries usually have a much lower fertility rate, often correlated with greater wealth, education, urbanization, or other factors. Mortality rates are low, birth control is understood and easily accessible, and costs are often deemed very high because of education, clothing, feeding, and social amenities. With wealth, contraception becomes affordable. In countries like Iran where contraception was subsidized before the economy accelerated, birth rate also rapidly declined. Further, longer periods of time spent getting higher education often mean women have children later in life. Female labor participation rate also has substantial negative impact on fertility.

In undeveloped countries on the other hand, families desire children for their labour and as caregivers for their parents in old age. Fertility rates are also higher due to the lack of access to contraceptives, stricter adherence to traditional religious beliefs, generally lower levels of female education, and lower rates of female employment in industry. The total fertility rate for the world has been declining very rapidly since the 1990s. Some forecasters like Sanjeev Sanyal argue that, adjusted for gender imbalances, the effective global fertility will fall below replacement rate in the 2020s. This will stabilize world population by 2050, which is much sooner than the UN Population Division expects.[7]

United States[edit]

Map of U.S. states by total fertility rate (TFR) in 2013.
Period U.S. Total
Fertility
Rate[8]
1930–34 2.1
1935–39 2.0
1940–44 2.5
1945–49 3.0
1950–54 3.3
1955–59 3.7
1960–64 3.4
1965–69 2.6
1970–74 2.1
1975–79 1.8

The total fertility rate in the United States after World War II peaked at about 3.8 children per woman in the late 1950s and by 1999 was at 2 children. This means that an imaginary woman (defined in the introduction) who fast-forwarded through her life in the late 1950s would have been expected to have about four children, whereas an imaginary woman who fast-forwarded through her life in 1999 would have been expected to have only about two children in her lifetime. The fertility rate of the total U.S. population is just below the replacement level of about 1.9 children per woman.[9] However, the fertility of the population of the United States is below replacement among those native born, and above replacement among immigrant families, most of whom come to the U.S. from countries with higher fertility than that of the U.S. However, the fertility rates of immigrants to the U.S. have been found to decrease sharply in the second generation, correlating with improved education and income.[10]

World extremes[edit]

The lowest TFR recorded anywhere in the world in recorded history is for Xiangyang district of Jiamusi city (Heilongjiang, China) which had a TFR of 0.41.[11] Outside China, the lowest TFR ever recorded was 0.80 for Eastern Germany in 1994.

Europe[edit]

The average total fertility rate in the European Union (EU-27) has been calculated at 1.59 children per woman in 2009.[12]

In the non-EU European post-Soviet states group to 2015, Russia has a TFR of 1.78 children per woman,[13] Belarus 1.70 and Ukraine 1.50.[14]

Factors[edit]

Further information: Sub-replacement fertility

A parent's number of children strongly correlates with the number of children that each person in the next generation will eventually have.[15] Factors generally associated with increased fertility include religiosity,[16] intention to have children,[17] and maternal support.[18] Factors generally associated with decreased fertility include wealth, education,[19] female labor participation,[20] urban residence,[21] intelligence, widespread birth control usage, increased female age and (to a lesser degree) increased male age.

See also[edit]

Dynamics:

Case studies:

Lists:

References[edit]

  1. ^ Total fertility rate definition from CIA world factbook. Cia.gov. Retrieved on 2012-09-17.
  2. ^ UNdata: Total fertility rate (children per woman). esa.un.org. Retrieved 2012-09-17. Archived June 7, 2012, at the Wayback Machine.
  3. ^ National Association for Public Health Statistics and Information Systems (NAPHSIS), "Statistical Measures and Definitions" [retrieved 16 June 2010].
  4. ^ "Field Listing: Total Fertility Rate". The World Factbook. Retrieved 2016-04-24. 
  5. ^ "Country Comparison: GDP - Per Capita (PPP)". The World Factbook. Retrieved 2016-04-24. 
  6. ^ Espenshade, T. J, Guzman, J. C., and Westoff, C. F. (2003). "The surprising global variation in replacement fertility". Population Research and Policy Review 22 (5/6): 575. doi:10.1023/B:POPU.0000020882.29684.8e. 
  7. ^ http://www.project-syndicate.org/commentary/the-end-of-population-growth
  8. ^ Ben J. Wattenberg (1985). "Chapter 11. The Birth Dearth". The good news is the bad news is wrong. American Enterprise Institute. ISBN 978-0-671-60641-1. 
  9. ^ http://data.worldbank.org/indicator/SP.DYN.TFRT.IN
  10. ^ "How Fertility Changes Across Immigrant Generations." Research Brief #58, Public Policy Institute of California, 2002.
  11. ^ Terrell, Heather Kathleen Mary, "Fertility in China in 2000: A County-Level Analysis" (2005), Texas A&M University.
  12. ^ Eurostat – Statistics Explained: Fertility statistics, Table 1 (data situation Oct 2011). Epp.eurostat.ec.europa.eu. Retrieved on 2012-09-17.
  13. ^ Russian Birth Rate above Regional Average, Euromonitor International, retrieved March 2013.
  14. ^ United Nations Statistics Division – Demographic and Social Statistics. Unstats.un.org. Retrieved on 2012-09-17.
  15. ^ Murphy, Michael (2013). "Cross-National Patterns of Intergenerational Continuities in Childbearing in Developed Countries". Biodemography and Social Biology 59 (2): 101–126. doi:10.1080/19485565.2013.833779. ISSN 1948-5565. 
  16. ^ Hayford, S. R.; Morgan, S. P. (2008). "Religiosity and Fertility in the United States: The Role of Fertility Intentions". Social Forces 86 (3): 1163. doi:10.1353/sof.0.0000. 
  17. ^ Lars Dommermuth; Jane Klobas; Trude Lappegård (2014). "Differences in childbearing by time frame of fertility intention. A study using survey and register data from Norway".  Part of the research project Family Dynamics, Fertility Choices and Family Policy (FAMDYN)
  18. ^ Schaffnit, S. B.; Sear, R. (2014). "Wealth modifies relationships between kin and women's fertility in high-income countries". Behavioral Ecology 25 (4): 834–842. doi:10.1093/beheco/aru059. ISSN 1045-2249. 
  19. ^ Rai, Piyush Kant; Pareek, Sarla; Joshi, Hemlata (2013). "Regression Analysis of Collinear Data using r-k Class Estimator: Socio-Economic and Demographic Factors Affecting the Total Fertility Rate (TFR) in India." (PDF). Journal of Data Science 11. 
  20. ^ David E Bloom; David Canning; Günther Fink; Jocelyn E Finlay. "Fertility, Female Labor Force Participation, and the Demographic Dividend" (PDF). National Bureau of Economic Research.  Working Paper No. 13583. Issued in November 2007
  21. ^ Sato, Yasuhiro (30 July 2006), "Economic geography, fertility and migration" (PDF), Journal of Urban Economics, retrieved 31 March 2008 

External links[edit]