so as you know by now populations can grow and they can decline but why says you well there are reasons and I reckon that's why you clicked on this video so if you're ready to get them brain cows milked let's get to it okay you'd better start by getting your vocabulary pants on because when geographers want to study Trends in population they consider three things fertility rates mortality rates and migration and hey if you want no guides to follow along with this video then check the link in the description so first fertility rates and this indicates a population's ability to have children and with these numbers governments for example can determine if their populations are growing or remaining stable or declining and why would governments want to know that well if they know how many babies are being born then they're better able to plan and allocate funds for infrastructure projects or education and Healthcare and I can see you're getting kind of antsy and you're like yeah but how do we measure fertility rates don't worry I got you boo there are in fact two ways to measure fertility rates and you need to get cozy with both of them first is the crude birth rate which is the number of live births per thousand people in a year so for example here in heimville if we have a population of a million and a hundred thousand babies are born then we divide this by this multiply by a thousand and we get a accrued birth rate or CBR of a hundred per thousand people now to be clear it's unlikely you're going to have to do these calculations on an exam but it is good to know how the math works so you can interpret graphs and charts Etc okay easy enough now here you see the spatial distribution of CBR across the whole world over here in North America we can see that they have a low birth rate which is a CBR of about 10 to 20. and then in several North African countries we see what we call a transitional birth rate which is a CBR between 20 and 30 per thousand and then down here on sub-Saharan Africa several places have a high birth rate which is a CBR greater than 30. so if heinfeld CBR is a hundred well you know we got babies for days anyway here's where I tell you that the crude birth rate is crude not because it indiscriminately drops colorful language at family dinners it's crude because it's not the most accurate measure of fertility rates and that's because it Compares births to the entire population including men and women of all ages so is there a more accurate measure of fertility rates you know there is and it's called total fertility rate which measures the average number of children one woman will have during her childbearing years which is to say 15 to 49 and the reason total fertility rate or TFR is a more accurate measurement is because it only considers the part of the population that is capable of you know bearing children okay now a TFR of 2.1 is what we call replacement level fertility because that's the number of babies that are required to replace the two people that had them now not surprisingly these numbers correlate pretty well with what we saw in the spatial arrangement of the crude birth rate Europe's dfr averages to about 1.6 which if you recall the replacement fertility level means that Europe's population is not replacing itself and therefore it is declining other places like South Korea and Puerto Rico have even lower TFR numbers and they have entered the Shiny Happy World geographers like to call death spiral demographics but sub-Saharan Africa's TFR is around 4.6 which again babies for days okay so fertility rates help geographers measure population growth or decline but on the other end of the demographic Spectrum we've got another way to measure it and that's called mortality rates and that's just an indication of a population's rate of deaths and wouldn't you know it there are two ways to measure mortality as well first is the crude death ray which is the number of deaths per thousand people now despite its crudeness CDR is a more accurate measure of death than crude birth rate is a measure of fertility and that's because you know last time I checked regardless of gender or income or education or whatever everybody dies sorry to be a bummer but yeah it's true so currently the global crude death rate is about eight per thousand people back in 1960 it was 13 per thousand so what does that mean people are living shorter lives now no get back in your cabinet and keep studying the decrease in CDR means people are living longer lives today than they were in 1960. but why would that be well in general people have access to better nutrition better medicines clean water Etc and that means global life expectancy has increased but here's where I tell you that depending on the scale we're considering that generalization falls apart at a national and Regional scale life expectancies vary according to how wealthy a nation is like in some developed Nations the life expectancy is 80 years while in many developing nations it's more like 50 years okay now the second measure of mortality rates you need to know is the infant mortality rate which is the number of children who die before they reach the age of one per 1000 live births and what the IMR is really good at showing is a country's access to health care for example in places with a high infant mortality rate they tend to have less access to life-saving interventions for babies so you can see here that a lot of the world has low infant mortality rates but in sub-Saharan Africa the rates are pretty high which would indicate less access to medical procedures for infants and mothers now migration is also a major factor in population growth in Decline but we're going to consider that in depth later in unit 2 videos so we're just going to leave it there for now okay now let's pull all of this together when geographers want to explain the reasons for population growth and decline they use a measurement called the rate of natural increase which is the crude birth rate minus the crude death rate and this is relatively simple to understand if more people are being born than are dying then we have a high rni percentage and that means the population is growing like we saw in sub-Saharan Africa but if the number is lower or close to zero then the population is stable like it is in the United States but if the rni is negative like in Germany well the population is declining however one note on the rate of natural increase its main limitation is that it doesn't account for population growth or decline due to migration only people being born or dying like a country might have a negative rni but still experience population growth if lots of immigrants are coming in okay now a related measure for population is known as doubling time which is the amount of time it will take for a population to double if current growth Remains the Same a country like Nigeria is experiencing explosive population growth at around 2.6 percent per year and that means the doubling time will be about 27 years but on a slower growth country like like the United States at about point three percent per year the doubling time is going to be about 233 years Okay so we've talked all about how to measure population growth and decline but now let's finish by considering the factors that actually cause the growth and decline first there are social and cultural factors religion for example is a large size factor in fertility rate for example Roman Catholics and Muslims both reject the use of artificial birth control and so in countries where those religions are dominant they tend to have higher birth rates additionally in places where men and women adhere to traditional gender roles women are expected to stay home raise babies and make everybody sandwiches in some places like that more babies tend to be born second political factors influence population growth and decline because governments watch their population numbers real close they can introduce various population policies which either encourage more babies to be born or restrict them now if governments pass policies to encourage reproduction those are called pronatalist policies and you see those in stable or declining population on the other hand you've got anti-natalist policies which seek to reduce the number of babies born and as I mentioned in the last video China's one child policy is a great example of this and third population growth or decline can be influenced by economic factors see birth rates often decline during economic downturns when people are worried that they don't have enough means to care for more children but when the economy is good the birth rate often increases because people are more optimistic about the future but economics can also determine rates of migration if country a is crushing it economically But Country B is having a rough time economically migrants will often leave B to find work in a and thus increase the population Okay click here to keep reviewing my other unit 2 videos and click here to grab my video note guides which are really helpful if you want to get an A in your class but you just can't read that textbook I'll catch on the flip-flop I'm Laurent