The Gini coefficient summarizes the area gap

It ranges from zero toward one.

Gini equals the area between the equality line and Lorenz curve divided by the total triangular area below the equality line. Zero indicates complete equality. A value closer to one indicates greater inequality. It does not measure the average income level: two societies can have the same Gini and very different living standards.

Taxes and cash or in-kind transfers can change disposable-income distribution. A transfer payment is not payment for current production and therefore is not included as current output in national accounting, though it affects household resources. Marginal tax rates and benefit phaseouts can also alter work and saving incentives.

The Gini coefficient compresses the Lorenz curve into a single number. Let area A lie between the equality line and the Lorenz curve, and let A+B be the entire triangle below the equality line. Then

Gini=(A)/(A+B).

Perfect equality gives A=0 and a Gini of zero. As the curve bows farther away, A grows and the coefficient moves toward one. Real-world values lie between these endpoints. The measure does not literally require one person to hold every dollar before indicating high inequality.

Graph questions may provide shaded areas rather than raw household data. If A=0.14 and B=0.36, then Gini=0.14/(0.50)=0.28. Dividing A only by B would give the wrong result. When axes form a unit square, the total triangle beneath the equality line has area one-half.

A proportional income change

Every household’s income rises by 10 percent. Each group retains the same share of total income, so the Lorenz curve and Gini remain unchanged. The society is richer in absolute terms even though relative inequality is identical.

Different distributions can have the same Gini because one number cannot preserve every detail of a curve. One society may have more inequality near the bottom and another near the top. If Lorenz curves cross, their Gini values can still rank them, but that ranking reflects total area and can hide where the differences occur.

Measurement choices matter. Household size, taxes, transfers, capital gains, underreported income, and whether the unit is a person or household can change the estimate. Wealth is usually more concentrated than annual income and should not be discussed as if it were the same variable. International comparisons also require compatible definitions and data quality.

A lower Gini is not automatically a Pareto improvement. It could occur because lower-income households gained, because top incomes fell while no one else gained, or because composition changed. Equality and efficiency are distinct criteria. Policies can alter both distribution and incentives to work, save, invest, or acquire education. The empirical magnitudes matter.

For economics exam, read the direction carefully: a Lorenz curve closer to equality implies a lower Gini, assuming the comparison is otherwise valid. Do not infer average income, poverty, mobility, or fairness from the coefficient alone. It summarizes relative inequality-and only that.

Use direction checks before calculating. A transfer from a higher-income household to a lower-income household that leaves their rank unchanged generally pulls the Lorenz curve toward equality and lowers the Gini. A proportional tax on every income followed by no redistribution leaves all income shares unchanged. These comparisons often answer conceptual questions without an area calculation.