expenditures, including in particular classroom construction and maintenance.200 Yet, "transforming resources into outcomes" raises specific challenges (in other terms, to ensure that the money is spent efficiently, and the education provided is of adequate quality); and so does ensuring that the resources are used equitably -- for instance, reaching the poorest regions or addressing the education needs of the lowest quintiles of the population.201 Some of these problems could be addressed in the simplest of ways: by taking a rights-based approach to the delivery of services such as health, education, or housing. That means defining clearly the level of support that individuals may claim from the State, as well as the eligibility conditions; providing potential beneficiaries with access to remedies, before independent bodies including courts, so that they may challenge a refusal to provide the support they claim; and informing them about their rights. Such an approach, ideally, would be able to address questions of underinclusiveness or discrimination, or inadequate targeting of the efforts. Where the level of support or the coverage of the population are insufficient, the question however remains: which weight should be given to the argument that the State simply cannot dedicate more resources to the public programme in question? How are we to assess whether the State has done "enough", although it appears that its efforts are insufficient to meet the needs? Neither the UNDP's approach based on the human expenditure ratio, nor similar approaches as developed by WHO or Unicef, answer that question. These attempts do assist in setting targets; but they do not allow us to assess whether a State could do more. Obviously, if this is the purpose, the definition of needs by setting absolute figures (the per capita public expenses for healthcare, for instance, or the public expenses for each pupil attending primary education) is of little help. Defining a percentage of the country's GDP that should go to particular sectors is more useful in this regard. But is this the right measure of a country's ability to realize economic, social and cultural rights? That is the question raised by recent attempts to define an "achievement possibility frontier" for States, to which we now turn. 2. The Achievement Possibility Frontier One attempt to propose criteria by which to assess States' capacity to fulfil human rights is by Sakiko Fukuda-Parr and her collaborators. Fukuda-Parr, formerly a loan officer at the World Bank, later joined the United Nations Development Programme, for which she worked a number of years in Africa. As the Director of the Human Development Report Office between 1995 and 2006, she was a lead author of the annual flagship publication of the UNDP, the Human Development Report, which is best known for popularizing the "Human Development Index" as a measure of development alternative to GDP growth per capita.202 Now a professor at the New School in New York, she brings the human development perspective to human rights, seeking in her recent work to define a metrics through which to assess the fulfilment by States of their obligations towards economic and social rights, taking into account their capacity (in terms of resource availability) to do so. In a 2008 paper, Fukuda-Parr and her colleagues offer to assess whether a particular economic and social right is adequately fulfilled (z) by examining the ratio between the extent of rights enjoyment, as measured through socio-economic indicators commonly used in the development field (x), and State resource capacity, using GDP per capita as a proxy for such capacity (y), so that z = x / y.203 Under this 200 See United Nations Children's Fund (Unicef), The Investment Case for Education and Equity (New York, 2015) (Box 5: Model to compute the financial allocations needed to achieve universal primary education), at 44. 201 See, respectively, sections 3.5. and 4.2. of the Unicef report cited above. 202 The UNDP website describes the Human Development Index (HDI) as "a summary measure of average achievement in key dimensions of human development: a long and healthy life, being knowledgeable and have a decent standard of living", which should provide a measure of progress in development alternative to the growth of GNI per capita and thus may allow us to ask "how two countries with the same level of GNI per capita can end up with different human development outcomes": see http://hdr.undp.org/en/content/human-development-index-hdi (last consulted on 20 Dec. 2016). 203 Sakiko Fukuda-Parr, Terra Lawson-Remer and Susan Randolph, Measuring the Progressive Realization of Human Rights Obligations: An Index of Economic and Social Rights Fulfilment (The Human Rights Institute of the University of Connecticut, Economic Rights Working Paper Series, Working Paper 8, 2008) 13-15. The authors takes into account that the capacity to fulfil economic and social rights does not increase linearly with the growth of GDP per capita, however: a country A with a GDP per capita that is 10 times that of country B cannot be expected to perform ten times better on socio-economic indicators related to economic and social rights outcomes. This non-linear relationship between GDP per capita growth and development outcomes was initially noted in studies measuring the Physical Quality of Life Index (PQLI) -- a composite 43