 Philosophical interest in the measurement of inequality has recently risen (Temkin 1993). Most of this philosophical literature, however, tends to focus on defining the right foundations for an aversion to inequality. In particular, Parfit (1995) proposes to give priority to the worse-off not because of their relative position compared to the better-off, but because and to the extent that they are badly off. This probably corresponds to defining social welfare by an additively separable social welfare function, with diminishing marginal social utility (a social welfare function is additively separable when it is the sum of separate terms, each of which depends only on one individual’s well-being). Interestingly, if egalitarianism is defined in opposition to this “priority view” by the feature that it relies on judgments of relative positions, this means that egalitarian values cannot be correctly represented by a separable social welfare function. This seems to raise the ethical stakes concerning properties of decomposability of indices or separability of social welfare functions, which are usually considered in economics merely as convenient conditions simplifying the functional forms (although separability may also be justified by the subsidiarity principle, according to which unconcerned individuals need not have a say in a decision). The content and importance of the distinction between egalitarianism and prioritarianism remains a matter of debate (see, among many others, Tungodden 2003, and the contributions in Holtug and Lippert-Rasmussen 2007). It is also interesting to notice that philosophers are often at ease to work with the notion of social welfare (or social good, or inequality) as a numerical quantity with cardinal meaning, whereas economists typically restrict their interpretation of social welfare or inequality to a purely ordinal ranking of social states. Beside egalitarian and prioritarian positions one must also mention the “sufficiency view”, defended e.g. by Frankfurt (1987) who argues that priority should be given only to those below a certain threshold. One may consider that this view supports the idea that poverty indices might summarize everything that is relevant about social welfare.