To obtain (13), the social welfare function underlying the concentration index, we replace the
principle of income-related health transfers by the following condition: for all h ∈Kid, for all j,
and for all α>0, h + (−(2j−1)α)1αj0 ∈Kid implies h + (−(2j−1)α)1αj0∼h.We will refer to this
condition as the CI condition. The CI condition specifies a trade-off between the individual that is
best-off in terms of socioeconomic status and any other individual in society that leaves the policy