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Fertility (view source)

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"Period" measures refer to a cross-section of the population in one year. "Cohort" data on the other hand, follows the same people over a period of decades. Both period and cohort measures are widely used.

*'''[[Crude Birth Rate]]'''. The CBR is simply the number of births in a year divided by the midyear population, times 1000. Since 1972, the CBR for the USA has been fairly steady , between 14.0 and 16.0. To calculate it you need to count the number of births and know how large the population is.

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*'''[[General Fertility Rate]]'''. GFR is the number of births in a year divided by the number of women aged ~~15-44~~, times 1000. It focuses on the potential mothers only, and takes the age distribution into account. To calculate it you need age data.

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*'''[[General Fertility Rate]]'''. GFR is the number of births in a year divided by the number of women aged 15–44, times 1000. It focuses on the potential mothers only, and takes the age distribution into account. To calculate it you need age data.

*'''Child-Woman Ratio'''. CWR equals ratio of the number of children under 5 to the number of women 15-49, times 1000. It is especially useful in historical data. It does not require counting births. This measure is actually a hybrid, because it involves deaths as well as births. (That is, because of infant mortality some of the births are not included; and because of adult mortality, some of the women who gave birth are not counted either.)

*'''[[Coale's Index of Fertility]]''' is a special device used in historical reseach.

===Cohort Measures===

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Cohort measures relate to a "cohort" of women (that is, women in the same age group). The cohort of women born in 1920 were aged ~~15-19~~ in 1935-39; they were 45-49 in 1965-69. Since we know the age specific birth rates in each of those years we can measure the cohort fertility. But consider the cohort of women born in 1970; they were aged ~~15-19~~ in years 1985-89; they were age 20-24 in 1990-1994; they will be aged ~~45-49~~ in 2025-29. Obviously we do not know what the future rates will be, so we have to wait a few decades. What impatient demographers do is create a "synthetic cohort"~~--an~~ imaginary group of women who have the same age-specific birth rates as we observe in a given year. The result is a snapshot of fertility in a single year (See Exercise 3 for how it works.)

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Cohort measures relate to a "cohort" of women (that is, women in the same age group). The cohort of women born in 1920 were aged 15–19 in 1935-39; they were 45-49 in 1965-69. Since we know the age specific birth rates in each of those years we can measure the cohort fertility. But consider the cohort of women born in 1970; they were aged 15–19 in years 1985-89; they were age 20-24 in 1990-1994; they will be aged 45–49 in 2025-29. Obviously we do not know what the future rates will be, so we have to wait a few decades. What impatient demographers do is create a "synthetic cohort"—an imaginary group of women who have the same age-specific birth rates as we observe in a given year. The result is a snapshot of fertility in a single year (See Exercise 3 for how it works.)

*'''age specific fertility rate'''. ASFR = number of births in a year to women in a 5-year age group, divided by the number of all women in that age group, times 1000. Thus if there are 10 million women age 25-29, and they had 1,179,000 babies in a given year, then ASFR = 117.9. The usual age groups are 10-14, 15-19, 20-24, etc.

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*'''[[Total Fertility Rate]]'''. TFR is the total number of births over a lifetime for a synthetic cohort. In the USA since 1972, TFR has flyctuated between 1.7 and 2.0.TFR equals the sum for all age groups of 5 times each ASFR rate.<ref> Another way of doing it: add up the ASFR for age 10-14, 15-19, 20-24, etc, and multiply by 5 (to cover the 5 year interval).</ref>

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*'''[[Total Fertility Rate]]'''. TFR is the total number of births over a lifetime for a synthetic cohort. In the USA since 1972, TFR has flyctuated between 1.7 and 2.0.TFR equals the sum for all age groups of 5 times each ASFR rate.<ref>Another way of doing it: add up the ASFR for age 10-14, 15-19, 20-24, etc, and multiply by 5 (to cover the 5 year interval).</ref>

*'''Gross Reproduction Rate'''. GRR is simply the number of girl babies a synthetic cohort will have. Since 49% of American babies are girls, GRR = .49 x TFR. It assumes that all of the baby girls will grow up and live to at least age 50.

*'''Net Reproduction Rate'''. NRR starts with the GRR and adds the realistic assumption that some of the women will die before age 59; therefore they will not be alive to bear some of the potential babies that were counted in the GRR. NRR is always lower than GRR, but in countries (such as the USA) where mortality is very low, almost all the baby girls grow up to be potential mothers, and the NRR is practically the same as GRR. In countries with high mortality, NRR can be as low as 70% of GRR. NRR of course requires knowledge of the age-specific death rates, in addition to the age-specific birth rate, and the numbers of women in each age group. When NRR = 1.0, each generation of 1000 baby girls grows up and gives birth to exactly 1000 girls. When NRR is less than one, each generation is smaller than the previous one; in the 1990s, the NRR for the USA was slightly under 1. When NRR is greater than 1 each generation is larger than the one before. NRR is a measure of the long-term future potential for growth, but it usually is different from the current population growth rate.

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What are the motivations for wanting ("demanding") fewer children. First of all they are expensive, especially in urban settings. Second, as a society modernizes and develops a complex infrastructure, large families are at a disadvantage compared to small ones. When family resource are concentrated on a few children, they are likely to do better than when resources are spread over many children. Schooling is an example; two children who attend secondary school can be more effective in a modern society than six illiterate children.

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A model of three preconditions for fertility decline was developed by demographer Ansley Coale. He asked what perceptions of the world were necessary if people were to consciously limit their fertility. a) Accept calculation, planning, and choice as valid (and thereby turn away from fatalism or the sense that God or the stars predetermines everything.) b) Perceive the advantages of having fewer children. However, families may perceive advantages and disadvantages in a very different way from government officials or outside experts. There are two factors here: whether or not fewer is better; And how people perceive advantages and ~~disadvantages--who~~ do they look to for the norms and standards of behavior? c) Know about and be able to master effective contraceptive techniques. This is the easiest part.

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A model of three preconditions for fertility decline was developed by demographer Ansley Coale. He asked what perceptions of the world were necessary if people were to consciously limit their fertility. a) Accept calculation, planning, and choice as valid (and thereby turn away from fatalism or the sense that God or the stars predetermines everything.) b) Perceive the advantages of having fewer children. However, families may perceive advantages and disadvantages in a very different way from government officials or outside experts. There are two factors here: whether or not fewer is better; And how people perceive advantages and disadvantages—who do they look to for the norms and standards of behavior? c) Know about and be able to master effective contraceptive techniques. This is the easiest part.

===Innovation-diffusion and "cultural perspective".===

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Historically societies that have low fertility now formerly had high fertility. Using the Coale model we can see that people have to learn how to control their fertility. Typically, low fertility is a cultural value that originates in the more privileged classes and then diffuses throughout society. In each community and social group there are innovators who are the first to experiment with any new idea or technique; they tell their friends and family, who are the secondary adopters. The mass media may speed up the process. In the USA, the "Comstock Laws" made it illegal until 1970 to publish information about contraceptives or to send devices through the mail.<ref> The Comstock laws forbidding pornography involving children are still in effect and rigorously enforced.</ref> Family physicians quietly informed married couples about withdrawal and condoms. Until the 1970s abortions were illegal and for most women hard to obtain. American feminist [[Margaret Sanger]] (1883-1966) crusaded tirelessly to promote knowledge about birth control and family planning. She wanted sexual liberation for women, and to attain that they needed control of their reproductive functions. She recommended the diaphragm, which gives the woman more control.

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Historically societies that have low fertility now formerly had high fertility. Using the Coale model we can see that people have to learn how to control their fertility. Typically, low fertility is a cultural value that originates in the more privileged classes and then diffuses throughout society. In each community and social group there are innovators who are the first to experiment with any new idea or technique; they tell their friends and family, who are the secondary adopters. The mass media may speed up the process. In the USA, the "Comstock Laws" made it illegal until 1970 to publish information about contraceptives or to send devices through the mail.<ref>The Comstock laws forbidding pornography involving children are still in effect and rigorously enforced.</ref> Family physicians quietly informed married couples about withdrawal and condoms. Until the 1970s abortions were illegal and for most women hard to obtain. American feminist [[Margaret Sanger]] (1883-1966) crusaded tirelessly to promote knowledge about birth control and family planning. She wanted sexual liberation for women, and to attain that they needed control of their reproductive functions. She recommended the diaphragm, which gives the woman more control.

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==High Fertility Countries: India, Ghana, Jordan==

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==High Fertility Countries: India, Ghana, Jordan==

The need to replenish society is a major cause of high fertilty. Before World War Two, mortality was so high in India that they needed the very high CBR of 37 (37 births a year per 1000 population) just to stay even (ie to keep a NRR of 1.0). In addition there was a strong commitment to the idea of the lineage. Everyone had a duty to ancestors and descendants to keep the line going, and indeed to maximize its strength or numbers. Thus there was a demand for high fertility.

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India before the 1950s, practiced natural fertility. There was very little birth control of any kind; fertility varied somewhat by education, but by no other social factor. The custom of very early arranged marriages (at age 12 or 13 for girls) increased fertility. Young widows were not allowed to remarry, which reduced the birth rate.

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==Low Fertility countries: USA, Japan, Britain==

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==Low Fertility countries: USA, Japan, Britain==

Low fertility countries have already undergone the demographic transition, and usually have also modernized their economy.

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'''[[Baby boom]]''': fertility fell steadily in the USA, from 1800 to 1940. Then suddenly it started going up again, reaching a new peak in 1957. After 1960 fertility started declining rapidly. In the Baby Boom years (1940-1964) women married earlier and had their babies sooner; the number of children born to mothers after age 35 did not increase. After 1960 ideal family size fell sharply, from 3 to 2 children. Couples postponed marriage and first births, and they sharply reduced the number of third and fourth births.

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In the United States in 1995, there were 110 live births per 1,000 women ages ~~20-24~~. Four decades earlier near the peak of the Baby Boom in 1958, there were 258 live births to women in the same age range.

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In the United States in 1995, there were 110 live births per 1,000 women ages 20–24. Four decades earlier near the peak of the Baby Boom in 1958, there were 258 live births to women in the same age range.

====Easterlin Model====

American Economist [[Richard Easterlin]] developed an ingenious model or theory to explain the Baby Boom. He assumes first that young couples try to achieve a standard of living equal to or better than they had when they grew up. This is called "relative status;" in other words, young men in one cohort compare themselves now to where their own fathers in a previous cohort had been. Second Easterlin assumes that when jobs are plentiful, it will be easier to marry young and have more children and still match that standard of living. But when jobs are scarce, couples who try to keep that standard of living will wait to get married and have fewer children. For Easterlin, the size of the cohort is a critical determinant of how easy it is to get a good job. A small cohort means less competition, a large cohort means more competition to worry about. The assumptions blend economics and sociology, and they seem to make sense, but notice that Easterlin did not rely on surveys or interviews asking people what really motivated them.

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Now to put the model to work. In the 20 years after World War Two, 1945-1965, the economy was strong and growing and demanded workers. But immigration was slight, and social custom prohibited most young mothers from working. Most important, the cohort (or number of people coming of age each year) depended on the number of births 15 or 20 years earlier, which was small. In 1940, there were 5.7 million men age 20-24, in 1950 there were 5.6 million, but in 1960, with a much larger economy, there were only 5.3 million. Employers scrambled to hire those young workers, and paid them well, enabling them to start families young. Furthermore, these men grew up in the Depression, and so there expectations of a standard of living were modest. Hence the Baby Boom. By the late 1960s times were changing. More immigrants were arriving (because of the new laws in 1965), mothers were now "allowed" to work (social customs changed drastically), and most important, the first of the Baby Boomers started flooding the job market (cohorts became larger). Thus by 1970 there were 7.8 million men aged ~~20-24~~. They had much more competition for jobs (from each other, the mothers and the immigrants), AND they grew up in the more affluent 1940s and so had higher standards to meet. (Easterlin also notes that they were crowded growing up, and had to compete for attention with siblings in large families and classmates in crowded schoolrooms.) Their solution was to delay getting married (perhaps by staying in school), and when married to have the mother work and to bear fewer children. Divorce was high because it was harder to make a marriage work. Indeed, the stress contributed to all sorts of other social problems, such as suicide and crime. Easterlin's model explains the Baby Boom very well. He and his students used it to explain the fertility changes in the early 19th century, when America was an agricultural society and to get married a young man had to have a farm. They tried to show that long-term cycles existed. When farm land was readily available couples married young and had lots of children, but when land became scarce they married later and had fewer children.

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Now to put the model to work. In the 20 years after World War Two, 1945-1965, the economy was strong and growing and demanded workers. But immigration was slight, and social custom prohibited most young mothers from working. Most important, the cohort (or number of people coming of age each year) depended on the number of births 15 or 20 years earlier, which was small. In 1940, there were 5.7 million men age 20-24, in 1950 there were 5.6 million, but in 1960, with a much larger economy, there were only 5.3 million. Employers scrambled to hire those young workers, and paid them well, enabling them to start families young. Furthermore, these men grew up in the Depression, and so there expectations of a standard of living were modest. Hence the Baby Boom. By the late 1960s times were changing. More immigrants were arriving (because of the new laws in 1965), mothers were now "allowed" to work (social customs changed drastically), and most important, the first of the Baby Boomers started flooding the job market (cohorts became larger). Thus by 1970 there were 7.8 million men aged 20–24. They had much more competition for jobs (from each other, the mothers and the immigrants), AND they grew up in the more affluent 1940s and so had higher standards to meet. (Easterlin also notes that they were crowded growing up, and had to compete for attention with siblings in large families and classmates in crowded schoolrooms.) Their solution was to delay getting married (perhaps by staying in school), and when married to have the mother work and to bear fewer children. Divorce was high because it was harder to make a marriage work. Indeed, the stress contributed to all sorts of other social problems, such as suicide and crime. Easterlin's model explains the Baby Boom very well. He and his students used it to explain the fertility changes in the early 19th century, when America was an agricultural society and to get married a young man had to have a farm. They tried to show that long-term cycles existed. When farm land was readily available couples married young and had lots of children, but when land became scarce they married later and had fewer children.

Unfortunately there are fatal problems with the Easterlin model. First of all, the sociologists have been unable to find the hypothesized motivations. Do people try to attain a standard of living similar to what they had when they were young by delaying marriage or manipulating family size? People deny it and the statistics for individuals show no effect. Do large cohorts in fact earn less than small cohort? The differences, over a lifetime, seem to be about 3% for men and 0% for women, so the effects are too small to be important. Easterlin theory's predicts an upturn in wages for young people entering the labor market in the 1990s (because they came from a smaller post-baby boom cohort). However, the wages seem to be lower, not higher. Do other countries show an Easterlin effect in their wage or fertility patterns over time? No. The theory seems to stop working circa 1980. With smaller cohorts trends toward lower fertility and lower wages were supposed to reverse themselves, but they did not. As Ronald Lee has concluded, Easterlin's grand theory now has few believers.

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===France===

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The French pronatalist movement from 1919-1945 failed to convince French couples of their patriotic duty to help increase their country's birthrate. Even the government was reluctant in its support to the movement. It was only between 1938 and 1939 that the French government became directly and permanently involved in the pronatalist effort. Although the birthrate started to surge in late 1941, the trend was not sustained. Falling birthrate one again became a major concern among demographers and government officials beginning in the 1970s.<ref>Andres Horacio Reggiani, "Procreating France: the politics of demography, 1919-1945." ''French Historical Studies'' Spring 1996 v19 n3 pp 725-54 </ref>

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The French pronatalist movement from 1919-1945 failed to convince French couples of their patriotic duty to help increase their country's birthrate. Even the government was reluctant in its support to the movement. It was only between 1938 and 1939 that the French government became directly and permanently involved in the pronatalist effort. Although the birthrate started to surge in late 1941, the trend was not sustained. Falling birthrate one again became a major concern among demographers and government officials beginning in the 1970s.<ref>Andres Horacio Reggiani, "Procreating France: the politics of demography, 1919-1945." ''French Historical Studies'' Spring 1996 v19 n3 pp 725-54</ref>

==Fertility in religions==

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One good example of the role fertility played in religion is the Israelites' use of pagan gods such as golden calves to bring fertility to the lands and their women. In most of Mesopotamia fertile land was essential to one's well-being and survival, so most pagan gods were devoted to fertility and growth.

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==See ~~Also~~==

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==See also==

* [[Birth Control]]

* [[Demographic transition]]

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* Lovett, Laura L. ''Conceiving the Future: Pronatalism, Reproduction, and the Family in the United States, 1890-1938,'' (2007) 236 pages;

* Mintz Steven and Susan Kellogg. ''Domestic Revolutions: a Social History of American Family Life.'' (1988)

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* Pampel, Fred C. and H. Elizabeth Peters, "The Easterlin Effect," ''Annual Review of Sociology'' (1995) v21 pp ~~163-194~~]

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* Pampel, Fred C. and H. Elizabeth Peters, "The Easterlin Effect," ''Annual Review of Sociology'' (1995) v21 pp 163–194]

* Population Reference Bureau, ''Population Handbook'' (5th ed. 2004) [http://www.prb.org/Reports/2004/PopulationHandbook5thedition.asp online] (5th ed. 2004), A quick 72pp guide to population dynamics; explains how to calculate and use major rates, ratios, and other measures from the birth rate to the life table; includes tips on interpreting population data.

* Reed, James. ''From Private Vice to Public Virtue: The Birth Control Movement and American Society Since 1830.'' 1978.

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Fertility (view source)

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