combined".116 A specific area in which action could be taken to widen the tax base in order to fund the realization of economic and social rights is by reducing, or eliminating entirely, favourable treatment granted to foreign investors in order to attract capital. There is in fact ample evidence that such "tax holidays" or even, more generally, legal protections granted to investors, have little or no impact on the ability of the country to attract investment.117 The major determinants of foreign direct investment (FDI) are economic factors such as the availability of skilled labor, market size and trade openness, as measured by exports and imports in relation to total GDP.118 For other variables there is less consensus in the literature. Generally however, the studies find that these political and economic factors are more important for the locational decision of foreign investment than the legal structure for protection of investors' rights and the ability to avoid double taxation by double-taxation treaties.119 In other terms, if there is one means through which revenues from taxation could increase rather painlessly (and at a relatively low administrative cost), it is by raising the taxes owed by foreign corporations operating in the country, or by closing loopholes, such as price transfer mechanisms, allowing such corporations to reduce their tax liabilities or even to entirely escape payment of local taxes. b) Implementing progressive tax policies The former Special Rapporteur on extreme poverty and human rights argued that States should be encouraged to "set up a progressive tax system with real redistributive capacity that preserves, and progressively increases, the income of poorer households. [A]ffirmative action measures aimed at assisting the most disadvantaged individuals and groups that have suffered from historical or persistent discrimination, such as well-designed subsidies or tax exemptions, would not be discriminatory. In contrast, a flat tax whereby all people are required to pay an equal proportion of their income would not be conducive in achieving substantive equality, as it limits the redistributive function of taxation".120 Her successor in the mandate, Philip Alston, emphasized this point further, regretting that we are still far from "recognizing the fact that tax policy is, in many respects, human rights policy", despite the obvious contribution taxation makes to the fulfilment of human rights: "The regressive or progressive nature of a State’s tax structure, and the groups and purposes for which it gives exemptions or deductions, shapes the allocation of income and assets across the population, and thereby affects levels of inequality and human rights enjoyment".121 It is time that these calls be heeded. Redistributive fiscal policies and social spending, particularly on social security, have made a major contribution to the reduction of the inequalities that would result from market incomes for different groups of the population. In OECD countries, public cash transfers, 116 Report of the Special Rapporteur on extreme poverty and human rights, Magdalena Sepulveda Carmona, presented at the 26th session of the Human Rights Council (A/HRC/26/28) (22 May 2014), para. 56 (citing ActionAid, Accounting for Poverty: How international tax rules keep people poor, 2009, at 5). 117 For a more systematic treatment, see Olivier De Schutter, Johan F. Swinnen and Jan Wouters, 'Introduction: Foreign Direct Investment and Human Development', in O. De Schutter et al. (eds), Foreign Direct Investment and Human Development. The Law and Economics of International Investment Agreements (London and New York: Routledge, 2012): 1-24. 118 A greater emphasis has been placed in recent years on the latter determinant as a result of globalization and the development of global supply chains. Even in this regard, however, the relationship is by no means automatic, as illustrated by the situation of Sub-Saharan African countries that are very open to trade but that nevertheless experience considerable difficulties attracting FDI. 119 The available econometric studies confirm the suspicion expressed by some in the legal literature (M. Sornarajah, 'State responsibility and bilateral investment treaties', Journal of World Trade Law, vol. 20 (1986), pp. 79–98; Jason Webb Jackee, 'Do Bilateral Investment Treaties Promote Foreign Direct Investment? Some Hints from Alternative Evidence', Virginia Journal of International Law, vol. 51 (2011), p. 397): there is weak evidence that the conclusion of investment agreements guaranteeing extensive rights to investors has more than a marginal impact on FDI inflows, and where it does seem to have some effect, it is mostly as a substitute for poor institutional quality, particularly in Sub-Saharan African countries or in transition economies swiftly moving towards open market policies. 120 Report of the Special Rapporteur on extreme poverty and human rights, Magdalena Sepulveda Carmona, to the 26th session of the Human Rights Council (A/HRC/26/28) (22 May 2014), para. 16. 121 Report of the Special Rapporteur on extreme poverty and human rights, Philip Alston, to the 29th session of the Human Rights Council (A/HRC/29/31) (26 May 2015), para. 53. 27