As time passes, outside of inflation, the buying power of an individual changes relative to their peers wealth.
How can I measure the effect wealth inequality has relative to one's savings?
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Economists generally think of three similar, but distinct, metrics of economic disparity: inequality of income, consumption and wealth. Income inequality is the most commonly cited measure, consumption inequality, though harder to measure, provides a better proxy of social welfare. Wealth is also an important metric since it can be inherited, unlike income. Most people would use the Gini coefficients to measure all three.
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