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 w