An industrialized exporter of agricultural produce in the second half of the 19th century, Denmark introduced social and labour-market reforms in the early decades of the 20th century, making the basis for the present welfare state with a highly developed mixed market economy. The Danish krone has been pegged to the euro since 1 January 1999. Denmark ranks as having the world's highest social mobility, the highest level of income equality,[11] and has one of the world's highest per capita income. For 2013, Denmark is listed 15th on the Human Development Index and 9th on the inequality-adjusted HDI. Denmark ranks highly positive on the Corruption Perceptions Index and the Legatum Prosperity Index, and as a full democracy on the Democracy Index.[13][14][15] It is frequently ranked as the happiest country in the world. Denmark is among the founding members of the NATO, Nordic Council, OECD, OSCE and the United Nations. There are three Danish heritage sites inscribed on the UNESCO World Heritage list in Northern Europe.