First, because, as explained above, it may provide a much too low standard of living in a country relative to what is considered freedom from poverty in that country. Second, because it may only identify the very poorest, which are not the sole object of anti-poverty policy in countries with substantially higher poverty as measured by national criteria, and with substantially greater potential for the mobilisation of domestic resources through redistribution. That is not to say that a policy maker would not want to know the effect of social policies on the dollar-a-day poverty headcount, but they may not be willing to judge the success or failure of social policy on that count alone. However such a solution is impractical, because it requires the definition, calculation and estimation of poverty depending on the group of countries studied. Moreover, if poverty has an inherent relative component, the necessity of using a common absolute poverty line is not borne out by either practice or theory. The preference for absolute, rather than relative lines to compare poverty between developing countries is often justified by the lexicographic relationship embodied in the "hierarchy of capabilities" described by Atkinson and Bourguignon (2001) and World Bank (1990).