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SEVERAL RECENT STUDIES OF POVERTY have demonstrated the usefulness of breaking down a population into subgroups defined along ethnic, geographical, or other lines [eg 1, 20]. Such an approach to poverty analysis places requirements on the poverty measure in addition to those proposed by Sen [15, 16]. In particular, the question of how the measure relates subgroup poverty to total poverty is crucial to its applicability in this form of analysis. At the very least, one would expect that a decrease in the poverty level of one subgroup ceteris paribus should lead to less poverty for the population as a whole. At best, one might hope to obtain a quantitative estimate of the effect of a change in subgroup poverty on total poverty, or to give a subgroup's contribution to total poverty. One way to satisfy the above criteria is to use a poverty measure that is additively decomposable in the sense that total poverty is a …