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Current time:0:00Total duration:9:01

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population dynamics looks at how the population of a country or region or even the world changes it takes into account the factors that increase a population and the factors that decrease the population to create a total growth rate there are three factors that contribute to this total growth rate these are fertility migration and mortality fertility is the natural ability of human beings to have babies and babies obviously add to the population migration looks at the number of people who are moving into and out of countries it doesn't change the total number of people living on the planet but it does change the number of people living in a specific country or region this doesn't mean that when you go on vacation to a different country that you are migrating their migration means that you are moving somewhere permanently to live and work and eventually die which brings us to our third factor mortality which is the fact that everyone eventually will die this obviously decreases the population in order to measure these three factors we use rates to measure the number of people who are born the number of people that move out of or into a different country and the number of people who die in a certain period of time usually we measure birth migration and death rates over a year's worth of population change because it is enough time that an obvious change is visible but not so much time that we miss trends and how the population changes and as human beings we tend to like nice round measurements like one year we almost a life's compare rates that are actually comparable so all these rates are measured per 1000 people this way we can compare the different rates equally because they are all scale to that same value a worldwide birth rate of about eighteen point nine births per 1000 people is much easier to grasp than looking at the around 134 million total births worldwide and is easier to compare country birth rates when they are scaled rather than looking at the total births take Molly for example where about 700 people will be born this year that doesn't seem like a lot compared to the 134 million births in the world but when scaled the birth rate in Mali is about 46 births per 1000 people which is more than twice the world average that's a pretty big difference all right so now that we've got some of the backgrounds and terminology out of the way we can look at what it is that affects population changes for this I'm going to just look at the population growth within a single country there are two factors that will increase the population of a country births and immigrations immigration is the movement of a person into a country conversely movement out of the country is called emigration but that decreases the population so I'll get to that in a minute as we've already seen birthrate is the number of births per 1000 people but another way to look at it is the total fertility rate which is the number of kids a woman is predicted to give birth to in her childbearing years that's why you hear of the typical family with 2.1 kids on average a woman in the US is predicted to give birth to 2.1 children in her life this means that the total population of the US will slowly increase a total fertility rate of exactly - neither adds nor subtracts from the population this is because the woman is giving birth to the number of people that created the children this rate only looks at the number of children a woman will bear so the two children exactly replace the biological parents and finally a fertility rate of less than two will decrease the population immigration as I mentioned before is the movement of people into a country this number is also scaled and again is measured by the number of people immigrating per 1000 people in the country if you want to look at the total population increase take the number of births plus the number of immigrations per 1000 people and there you go that is the rate at which people were added to the population now we can look at the factors that decrease a country's population and you guessed it death and emigration when we look at the number of people who have died we often refer to mortality rates which are the number of deaths per 1000 people you have to be kind of careful when looking at mortality rates especially when comparing the mortality rates of different countries just because the country has a high mortality rate doesn't mean there are a lot of young or unnatural deaths for this we can take a look at population pyramids a population pyramid graphs the age and sex distribution of a population on either side you have males and females and along the vertical axis you have increasing age if there are a lot of elderly people living in one country who are living a long time and dying of old age you get either a stationary or constrictive pyramid these kinds of population pyramids usually indicate low birth rates and low death rates throughout the population a constrictive pyramid indicates that there are fewer young people than old and is generally seen for very developed countries so the death rate of this country with lots of old people doesn't compare well to a country where perhaps people are dying young from disease this country's population can be modeled by an expansive population pyramid which indicates high birth rates and high death rates a better comparison is to look at age specific mortality rates so you can see how many people are dying within a specific age range now you can compare just elderly mortality rates between different countries or just the mortality rates for any specific age or age range save 20 to 24 year olds or 45 to 49 year olds there's a lot more information you can glean from age specific comparisons when you split up the mortality rates by age you can get what's called a life table or mortality table this table tells you the probability that someone will die given their age which can vary from country to country but when looking at the population of a single country an all-encompassing mortality rate is sufficient the second factor that decreases a population is the emigration of people to other countries just like all the other rates I've mentioned emigration rate is measured by the number of people emigrating per 1000 people in the country so if you take the number of deaths plus the number of immigrations per 1000 people you can get the rate which people are removed from the country sometimes it's interesting to look at just the migration statistics the net migration is the difference between the number of people entering the country and the number of people leaving the country there are many reasons for people to migrate from the country of their birth to a new country worldwide the trend is generally that people are moving to the more industrialized countries because of the potential for a better life some people leave their homes for political reasons and become refugees in a new country some people migrate for their jobs or because they just want to live somewhere foreign for many of these same reasons people will often move within their own country which is called internal migration while this doesn't change the total population of the country it can affect the economics or cultures of a country often internal migration is a large factor in urbanization as people move from rural areas to urban areas fertility migration and mortality all contribute to the growth rate of a country but remember that growth rate is not always a positive number if we want to look at this as an equation you have the initial population plus the number of births minus the number of deaths plus the number of people immigrating into the country minus the number of people emigrating out of the country so now you have your current population and if this current population is less than the initial population then you get a negative growth rate for that country so while our world population continues to grow the growth rate of some countries is in fact negative as more people die and leave that country then are born and move into it so as you can see there's a lot to consider when looking at how a population changes you can't just look at births or deaths alone you have to take into account that people move to different countries and even if you take into account every factor you can think of it is still only an estimate we can't go around to get a headcount of all seven billion plus people in the world we can try with surveys and records but in some countries even that just isn't feasible so we extrapolate a nest as well as we can so we can study how our populations are changing