Key Terms:
- demography
- rule of 70
- natural increase
- dependency load
- population growth rate
- population pyramid
- migration
- doubling time
The key to understanding this chapter is the formula for population growth:
population growth = natural increase (births-deaths) + net migration (immigration-emigration)
We study population as a predictor -- using simple linear regression to predict how many people there will be going forward. This is useful for us to know when it comes to calculating needs for services, infrastructure and also the country's ability to pay for entitlement programs like Old Age Security.
Looking far forward, we can use such information to establish good predictors of when population doubles (doubling time). The rule of 70 takes what we've learned from linear regression analysis and simplifies it into a very basic and reliable rule of thumb -- divinding 70 by the population growth rate will tell us how long it will take for the population to double. As an example, Togo's growth rate is 2.4%. If we divide 70 by 2.4, we can expect that Togo's population will double in 29.17 years.
We can also use graphical representations like a population pyramid to assist us in predicting how things will look in the future.
