Models tell you how the economy works on average. But averages hide who actually gets the gains, and they ignore the costs piling up off the books. This final unit turns from theory to the big real-world questions: who shares in growth, whether growth can last, and what history has taught us.
Start with the question of who gets what. Measuring inequality means putting a number on how unevenly income or wealth is spread across a population. Two countries can have the same average income while one is far more lopsided than the other. To see the difference, you need a tool that captures the whole distribution.
That tool is a pair of close cousins. The Lorenz curve plots the share of total income earned by the poorest 10 percent, the poorest 20 percent, and so on up to 100 percent. If everyone earned the same, the curve would be a straight diagonal. The more it sags below that diagonal, the more unequal the society. The Gini coefficient turns that sag into a single number from 0 to 1. Zero means perfect equality; one means a single person owns everything. A Gini of 0.25 marks a fairly equal country, while 0.55 marks a very unequal one.
Inequality also exists at two scales, and they have moved in opposite directions. Within-country inequality measures the gap between rich and poor inside one nation, which has widened in many rich countries. Between-country inequality measures the gap across nations, which has narrowed as China, India, and others caught up. Whether inequality is rising or falling depends entirely on which scale you mean.
Growth raises a second worry. Sustainable development is growth that meets today's needs without robbing future generations of the resources and clean environment they will need. A boom built on burning through forests, fish stocks, and a stable climate is a loan against the future that eventually comes due.
The hidden bill often takes the form of an environmental externality — a cost of production, like pollution, that falls on third parties rather than the polluter, so the market price leaves it out. GDP happily counts the factory's output while ignoring the smog it produces.
The unit closes with a tour of the great episodes in macro history. The Great Depression of the 1930s taught the danger of inaction. The 1970s stagflation broke the old Phillips trade-off. The Volcker disinflation of the early 1980s showed the brutal cost of crushing inflation. The 2008 global financial crisis revealed how fragile the banking system can be. And the 2020 COVID shock proved how fast a healthy economy can be frozen. Each crisis rewrote part of the textbook.