https://extranet.who.int/iris/restricted/bitstream/10665/71116/1/80%282%2997-105.pdf

There are, in short, many ways that governments can potentially influence both health gaps between the poor and better off, and the degree to which poor households are affected disproportionately by the costs of health services. The limitations are well known, and indices are available that respond to these limitations, by, for example, allowing the analyst to specify the degree of aversion to inequalities between the poor and better off. Standard-error estimators are also available, enabling significance tests to be undertaken on survey data, as are indices of "achievement". The latter capture not only the degree of poor-nonpoor in equalities but also the mean. Indices of the distributional impact of health spending are also available, which are firmly grounded in the literature on income redistribution and poverty. (Au)