What measure is commonly used to express income inequality within a population?

The Gini coefficient is a widely recognized measure for quantifying income inequality within a population. It is represented as a value between 0 and 1, where 0 indicates perfect equality (everyone has the same income) and 1 signifies perfect inequality (one individual has all the income while others have none). This coefficient effectively summarizes income distribution in a single number, allowing economists and policymakers to compare levels of inequality across different populations or track changes over time within the same population.

In contrast, the other measures listed do not serve this purpose. The Laffer curve illustrates the relationship between tax rates and tax revenue, demonstrating that there is an optimal tax rate that maximizes revenue without discouraging economic activity. Factor endowment refers to the resources available in a country, such as land, labor, and capital, which affect its ability to produce goods and services but do not measure income inequality directly. Tariffs are taxes imposed on imported goods to protect domestic industries or generate revenue, not a measure of income distribution. Thus, the Gini coefficient stands out as the correct answer for expressing income inequality.