Quantitative Aspects 
Quantitative Aspects
by Yale / Robert Wyman
Video Lecture 10 of 24
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Date Added: November 8, 2009

Lecture Description


Census data is often politically influenced and hence inaccurate. The birthrate in developing countries is nearly twice that in developed countries. Most humans live in less developed countries, so the world birthrate is near the higher number. The world birthrate is two and a half times the death rate; we are not close to population stabilization. Almost everywhere, the death rate has been drastically reduced; further changes will not massively affect demographic trends. Changes in fertility rate now control population. Demographic data must be corrected for age structure. A young population in a poor country will have a lower death rate than an older population in a richer country. Countries with high birthrates and exploding populations will have a high proportion of children. There are more people in each younger age bracket than in older ones. Many more adolescents will come into reproductive ages than older women will leave fertile ages. Fertility per woman is falling in the world, but, since there are ever more childbearers, the number of children born does not drop. Because of this 'momentum,' it can take over 100 years from when fertility falls to replacement level (approximately 2 children per woman) to when population stabilizes. In developing countries, even though fertility has been reduced, population growth often outstrips economic growth. People may give up on modernization and instead, idealize a return to some imagined past that was glorious.



Reading assignment:

"Family Portrait: A Clan Keeps on Growing." National Geographic (March 2001)



Weeks, John R. Population: An Introduction to Concepts and Issues, pp. 40-45 and 53-57




Transcript



February 17, 2009



Professor Robert Wyman: Let me start. I'm going to read you something and you have to guess what kind of a scene I'm describing.



"A ghostly stillness descended over the country, this country today, with every restaurant, bar and teahouse in the country closed. Every store shuttered and police patrolling the streets to make sure no citizen dare to step outside. Avenues normally clogged with traffic were so empty that picnics could have been held on them, except that nobody would have been allowed to attend. Plazas that are perpetual nightmares of congestion and exhaust fumes were abandoned to wandering dogs and cats. It was also a good day for the fish because the thousands of fishermen who line the shorelines on Sunday were all at home. The waterway itself, one of the world's busiest waterways, was as flat and silent as a woodland pond. The government decreed a six-month term--jail term for any citizen who didn't spend the day at home. All in all, the country today looked like a land on which a neutron bomb had been dropped devastating the population while leaving the buildings undamaged." What do you think it is? It's drastic.



Student: The plague?



Professor Robert Wyman: Nope, good, reasonable guess, but no. Governments weren't as strong then. It's the census day in Turkey. Some places take their census' very seriously and require that people really be in the place of their residence so that they can be counted and that they get a very good set of numbers. The waterway that they're talking about between Europe and Asia running through?



Student: The Bosporus.



Professor Robert Wyman: The Bosporus, right. Now compare this to another country. An educated and motivated guy got one of the temporary jobs as a census taker. He was high class enough to get an article published in The Atlantic Monthly. This is New York City. I'll tell you because you'll guess. He was 6'4" and Caucasian. They sent him to Chinatown. People took one look at him and slammed the door. Others offered him money to go away; even most of those who tried to cooperate did not have time to fill out the long form.



He asked to be assigned to another area. He got Wall Street. Same story, no one would cooperate with him. He couldn't even get into one building, but this was a motivated guy, like a Yalie. He climbed onto the roof of the next building, the building next door, he jumped over the partition, not across the street but over the partition -- to get into the building that he was supposed to take the census of. Right there on the roof was a dilapidated shack. Okay maybe someone's living in the shack.



He knocks on the door, someone inside flings open the door. Inside he could see several apparently naked people lying on hospital gurneys. The man who opened the door was wearing a white coat, "Go away!" He screamed, "I'm giving my wife a cancer treatment." New York City. A more experienced census taker told him that he wasn't doing it right. What you have to do is what they say, "curbstone it". What that means is you sit on the sidewalk and guess how many apartments are in the building. You look up at the building, you guess how many apartments in the building, and fill out that many forms with guesses about how many people live in each apartment. That's the way censuses are done in New York City, a comparison to Turkey.



Now these are describing the 1990 Census. I'll get to the 2000 Census in a moment. That census was the most expensive ever, it missed more than two million children, of course mostly minority children, and imagine what this does for school planning, etcetera, etcetera, it missed all together--not counting just children--ten million people and it double counted, or it counted in the wrong place another six million people. Between censuses the census bureau uses the count of the last census to make its projections. They know the population is increasing every year, how much do we have now, now, now?



By the time they came from the 1990 to the 2000 Census, there were seven million more people in America then the Census Bureau thought there was. The population had been increasing something like one and half times what they had thought it was. Does this slop matter? The poor quality of the United States census. Well, nowadays these numbers might seem small but more than $185 billion dollars a year in federal aid to states are apportioned according to the census results, so every state really wants its people counted. On top of that, what else is apportioned depending on the census? Congress, the House of Representatives is apportioned, so people want their state to have as many representatives as possible.



Given the importance of this, why is it so bad? Why is the U.S. Census so bad? The answer is primarily politics. It is well known, the kind of problems that this census taker had in New York is very well known, and it's well known that these people that are considered somewhat marginal: minorities, immigrants, poor people, they are heavily undercounted. This is well known. The problem is that these people don't vote Republican and when this story that I'm telling you takes place, the Republicans controlled the House of Representatives, which controls the budget.



The census has been missing this eight--ten million for the 1990 Census, eight million for before, roughly eight to ten million people, and again, it's these minority groups, minorities, renters, urban dwellers, and so Democrats--and they generally vote Democrat--and the Democrats have been pushing to get them counted, to make an accurate account. But a Republican redistricting expert wrote a memorandum in 1997 predicting that adjustment could cost the Republican Party 24 house seats, which is a huge amount. So, since then, the Republicans have blocked any modernization of the census.



For the year 2000 Census, President Clinton appointed a new director of the Census Bureau, a woman named Martha Riche who we've had here at Yale. She came out of a scientific and research environment and was really very competent, scholarly, knew how to do it right, and she announced when she came into office, "All industrial democracies will be holding a census in the year 2000. We want the United States to win a gold medal for accuracy." She thought she was smart. In fact of course she missed the boat, because she thought she was supposed to make an accurate census, and no, that wasn't what she was hired for.



What she had proposed was a statistical way of dealing with this. You know the groups that you've missed, you know where they live, so after you've counted everyone as well as you can in the whole country, you go back to the inner city neighborhoods, the various places where you know that you're going to miss people and you really blanket that and do--those areas very carefully, a sample across the country. Then you find out what your errors are in that large sample and then you can adjust the whole population, assuming you made the same mistakes everywhere.



She was very open, that's what she planned to do. At the time, though, Newt Gingrich, I don't know if you know that name with the New Deal for America or something, was the Speaker of the House, controlled the budget, and he said, 'yup, you have the authority to do that, you're the Director of the budget [correction: Census], but, if you do that, I will cut your budget to zero.' Basically she wasn't allowed to do that and so she had to resign. She just would not do a census that was less then what we're capable of doing.



The census was done the old fashioned way, it cost $1.7 billion dollars more than it would have with sampling and was not anywhere near as accurate. Now these same considerations apply almost everywhere. In China, for instance, you know about the one child policy and the government is strongly trying to push the birthrate down. We'll talk about this later in much more detail. A provincial official gets the word this is--we want your population growth rate to be no more than whatever percentage and then he sends it down to the prefecture and down. Do you think any of these officials, after the census, are going send up information that they have not been doing their job, that the birthrate is higher? No, so there's problems with that.



Who collects this data? Well luckily several--many organizations collect the data but primarily the UN. Who owns the UN? Member countries, and if you are, say, a conservative religious country, and if the UN demographer says that contrary to government statistics, that there actually is a high rate of illegitimacy or abortion in the country, all of which comes out of the statistics, they're not going to allow that to be published, so the UN has to sort of cut some corners so that the countries from who it is dependent on to get the data, will continue to send them the data.



In addition, even when a country tries, there are something like 50 million--birth registrations not done everywhere in the world and there's something like 50 million babies, worldwide, who were never registered, they don't exist on the official registers, so when you try to do what demographers do, you have a count of--a count of a census in one year, you have a count of a census in a later year, in between you have a list of births and deaths, supposedly both births are registered and deaths are registered, and you see is this reasonable? Is the difference accounted for by births, deaths, and migration if you have reasonable amounts of migration. If millions of the babies are just not registered you can't check things that way, so there's a lot of problems.



Another thing is that in many, many countries there's conflict between different groups, we've talked about Democratic, Republican in the United States. In Nigeria, in Sudan, there's a huge conflict between the Muslim populations in the north and the Christian or Animist populations in the south. You may or may not recall the Biafra War in Nigeria, a huge war between basically--over oil--but between the Muslim north and the Christian south; millions of deaths and millions of deaths now currently in Sudan over something of a similar issue.



When censuses in ethnically or religiously split countries are taken, the key event is the ratio, the key outcome that everybody wants to know is the ratio between how many Christians, how many Muslims, how many this, how many that. And so the censuses get totally distorted by people trying to raise their numbers and lower everyone else's numbers. Before the Biafra War there was apparently a reasonably accurate census in 1952 to 1953, then the Biafra War intervened, and the next several censuses were very controversial.



So the accepted official figures, in Nigeria, were 88.5 million people, but the World Bank said, no, that's wrong, 102 million people. The United Nations: 120 million people. So, basically, for a country as big and as important as Nigeria for their last census we have figures ranging between 88.5 million and 120 million, a 50% uncertainty for Nigeria, so big. The point of this initial part, point one, is that even the simplest numbers like headcounts, we're not doing anything fancy, we're just trying to count how many people there are, 1, 2, 3, 4, 5, there are systematic errors and very often those errors are intentional.



Now all of these numbers--well I say when I described these numbers and I probably won't do it enough. When I put up a demographic number it should almost always be qualified by, 'and there are large and unknown error bars,' but we don't have error bars for it.



Various organizations collect all this data and this is called the Population Reference Bureau, which is a source of statistics and news, everything about population and it's a very big sheet here. I'll show it to you blown up and it has every region of the world, every country of the world, and a large number of demographic statistics for each of these countries.



Let's look at one of these, so here is one page of this sheet--can you see that well enough? I don't need to put the lights out. What you see is the various numbers that they count, population, birthrate, death rate, rate of increase, migration rate, in or out, plus for coming in, out for going out, what their projected population is for 2025 or 2050, and so forth down there, a number that we'll try to get to describe later called the total fertility rate, which is more or less the number of children women are expect--will have as they go through their lifetime. Then on this side it's broken down first into the world, broken down by level of development, then by geographic region, so there are a lot of really very good data, very clearly put on here, and you can look first at the world's population here, so that's the first number in the whole thing.



This is the middle of 2008 so there were 6.7 billion people on earth and still rising. The expectation for mid-2025 is 8 billion and for 2050, 9.3 or 9.4 billion. Those are guesses about the future and I'll tell you maybe a little bit about how those are done. Look now at the birthrate here, so this is births per 1,000 population and the birthrate of the world is 21, and I'm going to go crazy going back and forth there. How accurate is that? Again we don't know, large and uncertain error bars, it's something like a third of the children in the world that don't have proper birth certificates and you can't know whether they've been counted at all.



Another thing that you should notice about the way it gets organized--is not only the world when it breaks it down into development categories there's less developed countries, that includes China and less developed countries excluding China. It's important to get those two things different because China is considered very exceptional, 1) because of its one child policy and they think that the birthrate is abnormally depressed, and 2) it's tremendous rate of economic development. If you want a real characterization of the less developed countries, even though China's average income is very low, it's changing very rapidly, then you do it without China and you get different numbers there.



Look next at the birthrate for--the birthrate for the whole world is 21 per 1,000 per year, and the birthrate for the less developed countries is 23, not a big difference. Why is that? How come it's so close? Whereas, for the developed countries it's 12, why is the birthrate for the world so close to the less developed?



Student: Because the majority of the population resides in those places.



Professor Robert Wyman: Right, the overwhelming majority of the population is in the less developed countries, so whatever we understand about that, that is what we have to--that is characteristic of the world. This difference in birthrate between say 12 in the more developed countries and say 23, 26, even 36 for the least developed countries, that is a huge difference. It's a factor of three between the most developed and the least developed, and a factor of something like 2.5--over 2 in between, which means that now most of the world is--in the underdeveloped countries most of the population and that will continue and will get more extreme.



Here is an example of that, this is--we are now about here and the more developed regions like the U.S. are still growing very slightly but basically going to be flat as far as one can project out here, but the less developed countries are undergoing this population explosion. If the ratio between the less developed countries and the developed regions is this now, that will only increase after 2050 out here. This--that the world is demographically characterized by the poor countries is a fact now, and a much better fact, as time goes on, a more complete fact.



That's--the first point is about inaccuracies of statistics, the second one here is that it's not the developed countries when you think of what's happening in world population don't think of the developed countries, what's happening is what's happening the underdeveloped countries or the developing countries.



Now let's shift and look at the death rate. We looked a little at the birthrate, and you notice something very interesting; here's the birthrate we've just been saying for the world 21 per 1,000 per year. Look at the death rate, eight, that means there's more than two and a half times in the world now--there's two and a half times as many births as there are deaths, an enormous difference and you can compare, in the less developed regions, there's something like three times as many births as there are deaths, 9 deaths, 26 births, so there's a huge--right now there's a huge imbalance between the births and the deaths.



As you know population stability, which many people think would be a good thing for the world, depends on the deaths and the births being equal, which means that the world is out of kilter, the ratio between births and deaths is now out of kilter by a factor of something like 2.5 to 3; 2.5 for the world, 3 for the developing countries. What that means is either the death rate has to come up to that level or the birthrate has to come down or some combination. Part of this is, well, we'll see--what's going to happen with part of it a bit later. The major point of this is that the world is very far from population stabilization.



You've probably heard lots in the news about declining birthrates in Europe, and Japan and so forth, and our next lecture will be about that, will be just about that. It's not characteristic of the world. The world is way out of balance, and even in the United States which is one of the few developing countries that still is having a population increase, we have 14 births for every eight deaths, and that's 1 and 3/4 times the number of births as deaths, so the United States is way out of whack, and that's births versus deaths. That doesn't include immigration. It includes the children of immigrants that are born in this country but doesn't include immigration, so our births plus immigration is going to be at least double our birthrate, so our population is also not anywhere near balanced.



Okay, now unlike the birthrate which is very different in different parts of the world, the death rate is not extraordinarily different. Here--I see you squinting; can you see it well enough? The death rate in the developed countries is 10 per 1,000 and in the less developed countries, again without China, it's 9 per 1,000, a very small difference. The reason for that is, is that mortality has fallen--because of vaccination programs, especially vaccination programs, oral rehydration for diarrhea and a lot of very basic public health matters, not open heart surgery or anything like that, but the most basic public health measures has dropped the death rate in the world tremendously, again especially the infant death rate.



Sub-Saharan Africa is somewhat of an exception to that. Anybody remember--maybe you studied it, what I said was sort of pre-modern death rate, somebody said it, I think they said it right; about 40 per 1,000 and now it's down to ¼ of that which is a modern rate and it's not going to decrease an enormous amount more. Fertility--so the changes in the death, when you look about the future of population, further changes in the death rate will have some effect but not an enormous effect. Its change in the fertility rate, the whole future world population depends essentially on the fertility rate.



A little bit from a change in the death rate, somewhat from people aging, but primarily fertility rate is what you watch to find out what's going to happen in the future of world population, unless of course we have atom bombs or something like that and everybody dies. Now as an example of this death--flatness of the death rate -- this is from Egypt, there's a lovely graph notice the little baby in swaddling clothes. This is from the Egyptian Statistical Abstract, the Egyptians published this themselves, and it's not the most recent. It goes up to about 1990 and maybe now they've gotten more computerized and don't dress the things up like that, but I just liked that and that color is the original color in the original statistical report.



Notice the number of births increasing continuously with some small dip here but basically it goes from 1,000 to up here would be 2,000. In this period of time the birthrate nearly doubles and this is absolute number of people, not a percentage, but look what happens in the death rate, very little change. The death rate, starting way back in 1952, so way before a lot of very modern kind of medical stuff, so it's basic medical--basic public health, basic sanitation that's responsible for this. So the number of deaths is staying more or less constant and of course the natural increase, the increase in the population is the difference between births and deaths, so you have it increasing every year, you get more and more population increase. This is the population explosion and you've seen numbers like that.



Now is the death rate staying constant? No, the death rate is not staying--because the population is increasing and yet you're having the same number of deaths, so the percentage of the population that's dying each year is going down slowly, not at a -- as a percentage -- it is a slow decrease, so over this period time period and continuing, the death rate is decreasing but not in a--significant enough to make a big difference in the total population growth statistics.



The basic thing in the world is that the fertility rate is what can change a lot, can make the difference between a world whose population keeps growing or stabilizes or starts decreasing.



Now, anybody notice anything funny so far? One number that should have--one pair of numbers that should have--what? Let's go back to that, anything funny about these numbers?



Student: The less developed countries have a little less.



Professor Robert Wyman: Yes, so the less developed countries have a lower death rate than the more developed countries. That's surprising that their health systems or their health is better than ours. Let's just check that number and let's look at for instance compare the United States with our neighbor, Mexico. We know Mexico is much poorer and probably doesn't have as good a healthcare system, well here's our deaths per 1,000 in the United States is 8; Mexico is 5, it's a good bit less then we have and further, here is Central America there's not a single country that's as high as we are. Every single one of the Central American countries, including some pretty poor countries, El Salvador has a lower death rate then the United States and Mexico is kind of in the middle between the 4 and the 6. Striking, you go further afield here, here's the Caribbean and these are more in the range of the U.S. level but they're--the U.S. is not better than almost any of them except for Haiti. Haiti is the only place that has a noticeably worse death rate then us.



Student: Do those death rates include the infant mortality rates?



Professor Robert Wyman: What?



Student: Do those death rates include the infant mortality rates?



Professor Robert Wyman: Yes, these are total death rates. Once you're born, if you die after you're born, you're counted. Don't include spontaneous or induced abortions. We got a problem here, what do you think is the reason for this?



Student: Because the United States has more older people than other countries.



Professor Robert Wyman: Exactly, the United States has more older people, and it's a funny thing about older people, they're the ones who tend to die. Once you get rid of your infant mortality issue, people tend to die at the older ages. That's exactly correct, and it's an extreme--in a developed country it's an extreme difference. Here is what's left, so this is the United States. This is the deaths per 1,000, the age of the people, and here's what's left of the infant mortality, it's still more dangerous to be an infant than later, but there's virtually--you can't even see the death rate through the middle years, but then boom it goes up as you get on into the older ages.



Indeed, the death rate is completely sensitive to your age distribution, a country that has more young people will have a lower death rate. A country that has a high birthrate will have more young people, will have a lower death rate, so what you're seeing in that anomaly there, what looked like an anomaly, is basically that Mexico has a higher birthrate of people. This funny thing, you happen to be born young and you die old, and so that is the explanation for that.



Any time--almost any demographic number that you want to interpret, marriage rates, birthrates, death rates, fertility rates, almost everything of interest is affected by the age distribution. In understanding demographic statistics, the most important thing is always the age distribution. You always have to pay attention to that, and later on I'll show you one of the mechanisms for paying attention--for getting statistics--adjusting statistics for the age distribution.



How--first let's just look at it. So here is the easiest way of looking at an age distribution. What you have here, this is for Germany and the pink is the old--this is 1989 when East and West Germany were still split, so this is the German Democratic Republic, East Germany, the pink is East Germans and the dark is the Federal Republic, West Germany, and on the left is men and on the right is female, male and female, and what this graph says is that every year--so this is age zero, you're just born, to age 100, that every year they ask how many people are there? How many kids are there between age zero and one? Well there's so many males and so many females, this number in East Germany, this number in West Germany.



You can go through every age and just count from your census the number of people at that age and draw it out like this. It's a wonderful huge amount of information in a single graph; you can see all kinds of things. This is World War I, the people born during World War I, they're almost all gone, but here's the ones from World War II and look at the big difference. Here's your females. Here's your males. What's the difference? War deaths; the men are in the Army and the get shot up on the Russian front, so you have many more females then males. It's partially that women live older also but this case in Germany is almost exclusive--is overwhelmingly the deaths from World War I, here there's still some females, there's no males, and then the deaths from World War II.



You can see the birth deficit, these are people who would have been born during World War I, these were adults, fighting age adults during World War I. These would have been born while the men were away so they didn't have any babies. They had very few babies during World War I and the same thing you see for World War II, and you see again the deficit of--well we talked about that.



You can see that, then you can see there's a post war baby boom, after the deficit in World War II people make up for it and more than make up for the deficit, so you have this huge bulge in population, both males and females, but now balanced, more or less equal numbers of males and females, and then you get the baby bust and you get a little echo effect, so there's variations--fluctuations in population--almost every country has--Western country has these kind of data plus the Asian countries that were involved in World War II. You can see it's a wonderful way of understanding a country.



Now this is India--the census of India, that's a weird one. What the heck is going on there? That's weird, so what it is, is people don't know their ages, they're innumerate, and so it gets counted every five or ten years, so here's a five year or a ten year period. They know their ages approximately, to approximately a certain year, they don't know it exactly. It's not important, in a pre-industrial country their exact age is not all that terribly important. You get this--that's called age heaping, that when you get a large excess in five or ten year increments.



My own father, who was an immigrant, did not know his age. There was--he was born in either 1904 or 1907 because he even had a birth certificate but it was in the Russian Cyrillic characters and the four looks like a seven, so he and my mother argued constantly over how old he actually was. Even countries that have had a long--European have the same thing. Here is the Soviet Union from their 1937 census and here again you get this same age heaping effect. Not quite as extreme as India but very clearly here, and to a degree worse with women then with men, because women are less educated, see the big bars here, the small bars here, and in principle it should be getting less with younger people it should be clearer, and you certainly do get rid of these extreme on certain of these but it's not--it's persisting into the 1930s this 'I don't know how old I am except within a five or ten year bracket.'



Here's another weirdo, what's that? Just to show you that you can immediately, once you get used to this, immediately tell an awful lot about a country from an age pyramid. Anybody from Arizona? Nobody from--what?



Student: [Inaudible]



Professor Robert Wyman: It's Sun City, Arizona which is a retirement community and they don't allow anybody--I think most of these have an age limit of 50, you have to be at least 55, so this is the retirement age, and where my mother lives in Century Village in West Palm Beach looks like this -- Florida looks like that, various retired--California has retirement villages they look like that.



These population pyramids are wonderful with lots of information packed into this and from seeing these pyramids you can tell a lot about the socioeconomic character of the countries because we know that the poor countries have less literacy, etc., etc., and they have higher birthrates and so we'll look at what that looks like right now.



Here are two of these population pyramids and here is--you saw in those the splitting of the world into more developed regions, and less developed regions. What do you notice right away? The total area under this, so this is now five-year age heaps rather than single year, so between zero and four is this amount, or this amount, so it's the area under this is how many total people there are. One you see there's a lot less area here, a lot less people, the less developed regions are the bulk of the world but also the shape is very different.



Here in the developed regions you have a more or less similar number of people in all ages. It's not exactly that way. Of course at the old age people are dying and that starts about here in the 50s and then accelerates and there's very few left, so it narrows here and also it's narrowing down here because the birthrate in the developed countries is now below replacement level and so the pyramids are getting to be fewer people in the younger ages then there are older people. Contrast that with less developed parts of the world and you see that there's more and more younger people, each age cohort has more and more people.



You can look at an individual country, and this is a clearer example. This is Nigeria as far as we can tell from their census, but they--you can tell an age distribution and this is now percent rather than total from sub-samples, you don't need to count absolutely everybody to understand what the age distribution is. Here is a 50-year change, there's not one--it's not changing very much. This is what it was in 1975, they know more or less what it is now, and they're projecting it out to 2005--;I'm sorry. This is pretty current and it looks about the same, and vastly as you go in this case, as you go to younger and younger people, vastly more children than older folks.



So what's happening here--see what the ages are here, especially in Nigeria, 15 to 45, these are the ages in which women are giving birth and this number of women is giving birth to more than two children, they're more then replacing themselves, so each bar is bigger than the last, and some of this in-swing, especially this is Sub-Saharan Africa, some of this reduction is infant mortality and child mortality. Some of the differences, especially between this bar and this bar, that's in there, but it's a small effect. The major effect is that every generation is bigger and they produce more and more children here.



Now--so when you look at how--what's going to evolve in the future--so here is your women who are 40 to 45, that's this bunch of women and women on this side, so that's the number of women. They're producing part of these children. In another five years, if you look at this five years later, these women who were 40 to 45 are now 45 to 50, no more fertility, pretty much. In Nigeria they're not using a lot of IVF and everything. So they have stopped reproducing but that cohort of that size is being replaced by the ones of this size coming into fertile ages, so women that were 10 to 15 are becoming 15 to 20 and starting their childbearing, when women that are 40 to 45 which have not so much childbearing left, are going out of existence and stopping childbearing absolutely.



The number of women, the number of child bearers is increasing drastically. In this case, it looks ballpark like there are twice as many women coming into reproductive age as are leaving reproductive age, each year, each five years however you want to count it. The number of childbearing women is increasing tremendously. The result of that is--here's another comparison, whereas in the west, in developed countries the number of 40 to 45 year olds is not enormously different then the number to 15 to 19. So the women that are leaving reproductive ages are more or less replaced by the women that are coming into reproductive ages.



Of course with population decline, eventually you get fewer women coming into reproductive age in developed countries then are leaving it, so that you have fewer child bearers, so this phenomenon can--if your population is increasing the problem gets more and more severe, if it's decreasing the problem gets more and more severe. There's a positive feedback on this with your number of child bearers either growing or decreasing.



Here is in billions--the number of women of childbearing age in the world, and it just keeps increasing, right? What you may be aware of, I haven't really talked about this much yet, because it's in my next lecture, here is the birthrate in the world, children per women. The birthrate has been coming down. Two opposite things are happening in the world. The number of childbearing women is going up but the number of children that each of them have is going down. They predict optimistically that by 2050 it'll reach about replacement of about two children per women, but it's not there, we're not there yet, we're almost double-- we're way above that now.



The result of this number of women rising, their rate of childbearing decreasing is that the number of births, you sort of multiply those two out, the number of births is expected to continue increasing for the predictable future. That the absolute number of births will increase as a result of these two crossing factors.



Now the birthrate is coming down and it eventually, let's presume in the future, gets to be two children. What then happens? You still have a pyramid like this but now it starts flattening out, but it flattens out--I should not do this by hand. In fact I want to go to this graph. It shows this--this is what's actually predicted to happen, so this is again developing countries and this is the kind of pyramid that we've seen. This one goes back to 1985 with this broadly increasing thing. It's basically a triangle, you can think of it is as a triangle.



If immediately, God sticks his finger out of heaven and says two children, and even more surprising, people obey him, what happens? This is the number of children, people that there are there, that the population pyramid will grow up but with this as a base, so that it will become square but there will be this many people. You go from a triangle to a rectangle with the same base. Can you see that? The number of people is the area inside that and you have the same base, you go from a triangle to rectangle--remember from high school geometry what the area is?



It doubles. Because, if you have a triangle and you go square, you just flip that--half the triangle over and you've got that many people again. If a miracle happens and fertility stops dead right now and we go immediately to two children per woman, the population doubles before it stabilizes. What this shows you, of course is that miracle is not going to happen. This is quite optimistic and is already not the case, that the base will also increase. Since the population is still increasing, the base will increase, and yes it will get more rectangular, but even by 2025 it won't yet be rectangular, so that you will, on this kind of projection, more than double the population from 1985 because the base is growing as well as you're rising up.



There's an expectation of quite a lot of population increase left. This whole phenomenon where because you--once you start having an increasing population you're going to--the population is going to keep increasing because there's more and more child bearers unless something drastic happens to the fertility rate, it's called population momentum because you're sort of moving in a certain direction of increasing population, it just continues.



The same thing happens as you'll see in the next lecture with population decreasing, and when population decreases you have fewer and fewer child bearers in each generation, as say Japan now or Singapore, and so unless the birth rate increases tremendously you'll have fewer and fewer children. What this shows you is that, if there's immediate replacement, this kind of miracle that everything--that everybody comes to just two children immediately, then the population would be this, so this effect is all momentum. All of this increase, from where we are now to up here, is just a momentum effect, just the fact that there's more and more children coming into reproductive age and that takes a very long time to work out. Then the fact that there's in fact -- they're not going immediately to two children, not immediate replacement. This is the United Nations guess as to what's going to happen. The actual population is projected to go like this.



If everybody immediately goes to two children you get this population rise. What is actually expected is somewhat more, so huge amount of what's happening with population future is already determined, it's already momentum is in there and even if birthrates really come down very rapidly, the world's population is going to continue increasing. That's sort of an important thing to remember. In the world the fertility is decreasing, the population is increasing and those are not canceling out.



From 1985 the prediction was that the world population would somewhat double, we've made some progress between there, but still we have 6.7 billion now and the expectation is something like 50% more people on earth in 2050 and perhaps continuing to increase beyond that. Huge amount of momentum effects, here is--let me go back--this is Mauritius, an island in the Indian Ocean and it's one of the examples of a small underdeveloped country that had a very surprising fertility decline.



This is probably the influenza epidemic here, but starting in around--right after World War II in the late 1940s, it's death rate fell down; modern public health comes in to Mauritius, so the death rate falls dramatically. Then this fits the standard characterization of the demographic transition. About 20 years later, about one generation later, people learn, well we don't have to have so many children because they're not dying, and the birthrate comes down thereafter and population growth is in here.



This is a country that did well, that starting fairly early for a developing country, 1951 say, their birthrate is falling down. They really sort of got it under control and--but look at this. So this is the birth--the total fertility rate which is a birth rate here, and it stays stable and then it starts falling down quite significantly, but look at here's total population size. You don't even see a change; all momentum. Here the birthrate has started dropping in 1965 and now we're 25 years later and you don't see hardly any change in the population growth rate.



That's what we talk about by the momentum effect that because at this time, before they drop their fertility, at this time there were so many more children than older people that the number of women child bearers just kept increasing and increasing, and increasing, so even though fertility drops the number of children stays high, even gets higher, and the population just keeps increasing. It's a very, very strong effect and the number of--and it's not flattened out there yet, 25 years later.



This is a projection of how long does it take before it flattens out. This is the first one, the first box is the year--this is our current size as of whatever year this was. By 2030--this is the United States. This is the number of people, so this graph was made in--it doesn't say the date but our population will increase somewhat by 2030 and this really is ignoring the changes that have happened with immigration and so forth that we will--we reach two child--if our fertility comes down we reach two child in 2030 and we stabilize because we have not had a rapidly expanding population so we stabilize right away.



Nigeria, which you saw, current population, it's supposed to but some optimistic assumptions reach two children per women in the year 2035, but then it doesn't stabilize until 115 years later at again a much increased population. In the case of Nigeria, after it reaches two child per woman, after it reaches replacement level, it takes another 115 years before population actually stabilizes. This is Bangladesh, 125 years. This is Iran, 110 years; Iran has had a big crash, we'll talk about that and its population. Brazil 145 years, it takes an enormous amount of time for momentum to work itself out after the fertility rate comes down. It's quite striking, and that's the reason why we expect so much more population growth to happen.



Again, you can look at an individual country, and this is Algeria, and look at what Algeria has done between--in 20 years: that's an enormous rate. Here's its crude birthrate, it's--crude means not corrected for age or anything, just take 1,000 people, how many babies were there for that 1,000 people. In 1965 there were 50 and it dropped to 38, a very large drop and it's a drop of 24%. They cut their birthrate by a quarter, that's 25% in 20 years, that's more than 1% a year, so there's a very, very rapid change.



Because of momentum the population growth rate was 2.4% in 1965 even though the birthrate is going down the population growth rate is going up, all momentum, and the percent of change that the growth rate increased by 19%, again all of this, because at this age, they had been having a population explosion, so many younger children than older. The population almost doubled from 12 million to 22 million, population went up 83% and the annual population growth rate increased from a quarter million to 600,000; 0.6 million, it changed 217%.



Here's the dilemma for developing countries, that basically all the developing countries understand that they need--that economically they'll be destroyed if their population growth rate increases and virtually every developing country has now an official national policy of trying to get its birthrate down. We'll see later that that's okay with the people, they're generally in accord with this, and they can do wonder--they can do miracles.



These countries--you'll see some of the drops next time, I'll talk about--next time in my lecture I'll talk about some of the fabulous drops. I mean this is not exceptional, this is a very significant drop but it's not exceptional around the world, and yet, even in the face of that, their population goes up into massive amounts, 83% up, 100% up, more than somewhat. As the government is pushing modernization, and as the government is pushing reducing the birthrate, and as grass roots organizations push to try to get the birthrate down, the population keeps increasing.



Industrial development, if it's not extremely rapid, can't keep up with the birthrate, so while these countries are modernizing they can see conditions deteriorate, poverty can grow, crowding can grow, homelessness can grow, again because population, even though you get your birthrate down, your population keeps increasing so extremely.



Some theory--believe that there's kind of a window of opportunity for the developing countries that, for instance, you take Egypt which I'm sure it's also had one of these drops not unlike this. They were kings of the world, top of the world in the Pharaoh's time, you all know that kind of history. Then iron was invented, but not in Egypt, and Egypt was in the bronze age during the Pharaoh's time. Iron is invented maybe in Turkey, I don't know exactly where and the other people's of the world picked up iron and made iron swords.



The Egyptians, for some reason, never really caught onto iron, maybe they don't have any iron anywhere there, and so from 1000 BC or something until 1950 they were always subject to somebody else. They were always ruled by someone else until Nasser got rid of the British in 1950, they were ruled by the British, and then before that by the Turks, and by all kinds of peoples, the Greeks before that--in Alexander the Greats time and so forth, and the Romans, they were ruled by someone else. Well here come--here's 1952 I think, Nasser's revolution, gets rids of the British, sets up an independent republic.



The people are very enthusiastic, they're very excited, they now throw off the shackles of imperialism, and colonialism, and they can now be their own country. But the birthrate is still very high, the population growth rate is very high, they have to industrialize real fast. They can't and they don't industrialize that fast, they don't modernize their economy. Why? A whole lot of reasons, one of which is they waste huge amounts of money on the conflict with Israel, that they have war after war, and have to spend huge amounts of money on the military that would be better spent on their economic development.



Time passes, and the people have tried to modernize, that's been the ideology, they've tried socialist modernization, they've tried capitalist modernization, and what they see is more and more crowding, poverty is not going away. Conditions are not getting very much better. I mean they do get a little bit better, but not terribly much better and so they give up on modernization. When they give up on modernization they glorify the past, they say it was better in the past, and they go to a romantic attitude to what it was like in--and can try to reverse modernization by resisting further drops in birthrate, for instance, going back to religion.



When I was in Egypt some years back, went into some sort of a restaurant and they seat you sometime at long tables, so people you don't know you sit next to, and if they happen to speak English I could talk to them, I don't speak Arabic, and so the ones that I could talk to were upper class--educated people and therefore upper class people that spoke fairly good English.



And you meet this nice young woman and she was at the University of Cairo which is an elite school, and she was an engineering student, so perfectly intelligent, perfectly modern in that way, wearing a head scarf, which her mother did not wear which was not in the previous generation. That she doesn't believe in modernization basically. For her own self-benefit she'll become an engineer because she wants a decent job. She doesn't want to herself go back and dig in the desert dirt there to try to get some food. She wants to be a modern person with a good job, at least she wants a good job, but she doesn't believe in modernization.



The rest of her ideology, aside from her personal desires, is backward looking, that things were better in the past, modernization has not worked. This is--there's this window of opportunity when countries first try to get modernized and one of the things that goes along with modernization is a reduced fertility rate. If it doesn't work people will reject that. A lot of what's going on in the world today with respect to the developed and underdeveloped countries, and the Arab countries, and the Western countries, has to do with this rejection of modernization because it did not work for them.



With that, if the birthrate stays high as it has, not in the Muslim countries. Many Muslim countries have had fabulous progress, but in a lot of the Arab countries the birthrate has stayed very high, and there's these huge numbers of unemployed young men, the economy cannot absorb them, they're hanging around, they're idealistic as all young men are, and what ideals do they pick up but going back to some imagined past that was glorious.



The world may hinge on this window of opportunity. How many countries can take advantage of it? China clearly took advantage of it, Japan took advantage of it. A lot of the East Asian countries took advantage of their window of opportunity, a lot of other countries did not take advantage of their window of opportunity.



[end of transcript]

Course Index

Course Description


This survey course introduces students to the important and basic material on human fertility, population growth, the demographic transition and population policy. Topics include: the human and environmental dimensions of population pressure, demographic history, economic and cultural causes of demographic change, environmental carrying capacity and sustainability. Political, religious and ethical issues surrounding fertility are also addressed. The lectures and readings attempt to balance theoretical and demographic scale analyzes with studies of individual humans and communities. The perspective is global with both developed and developing countries included.



Course Structure:

This Yale College course, taught on campus twice per week for 75 minutes, was recorded for Open Yale Courses in Spring 2009.

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