متریک برای ارزیابی "مزیت" توزیع درآمد و اثر تغییرات قیمت

Social welfare evaluation depends in part on value judgments as to income distribution. This paper proposes a metric for assessing the “goodness” of particular income distributions. That metric is then used to examine the effect of price changes on the “goodness” of a given distribution. Consider an increase in the price of a commodity that is disproportionately consumed by households with incomes that are high relative to the preferred income distribution. One naturally supposes that such a price increase will make the given income distribution appear less bad. Surprisingly, this is not invariably the case.

As is well known, social welfare evaluation of different allocations of commodities to individuals depends in part on value judgments as to income distribution. In this paper, I propose a metric for assessing how good or bad a particular income distribution is thought to be. I then go on to use that metric to examine the effect of price changes on the “goodness” of a given distribution of money income. Consider an increase in the price of a commodity that is disproportionately consumed by households with incomes that are high relative to the preferred income distribution. Since what matters to welfare and to welfare judgments is real, not money income, one naturally supposes that such a price increase will make the income distribution under consideration less bad. Surprisingly, this is not invariably the case.

This paper has proposed a natural-seeming metric for evaluating income distributions. That metric compares the total income required to achieve a given level of welfare when income can be reallocated to that required when reallocation is impossible and income distribution is fixed. But the very fact that one can measure “goodness” of income distribution in terms of trade-offs with total income leads to a somewhat surprising result when one considers the effect on the metric of an increase in a particular price. As one would expect, such an increase affects the evaluation of a particular income distribution by altering the distribution of real income in favor of households consuming relatively less of the good whose price has risen. (In the case of an egalitarian value judgment, this will improve the evaluation if the good in question is consumed relatively more by the rich than by the poor.) But this is not the only effect. Changes in income distribution have an impact on social welfare not merely in terms of fairness but also because they affect total consumption of individual goods and the total income level required to offset poor distributions. This means that an increase in a given price will also make it relatively more expensive to compensate for a poor income distribution if total consumption of the good whose price has risen is greater relative to total income at that distribution than at the preferred distribution. This will tend to be the case whenever the redistributive effect is favorable, since, in that case, those who are unduly rich at the poor distribution will also tend to be those who consume more of the good in question. Hence, even in the simplest cases, there are usually off-setting effects, and quantitative, rather than qualitative evaluation is required.