An autonomous revenue authority also has begun operation, improving collections and accountability. Cassiterite production peaked at 1,000 tonnes in 1990, but was under 700 tonnes in 2000. Recorded coltan production has soared from 147 tonnes in 1999 to 1,300 tonnes in 2001, and coltan was the country's biggest single export earner in 2001. At least part of the increase in production is because of new mines opening up in Rwanda. However it is true, as has frequently been observed, that the increase is also because of the fraudulent re-export of Congolese coltan. In addition to the well-publicised involvement in this trade of the Rwandan Defence Force (RDF), another important factor in the coltan re-export is that international dealers are under pressure not to buy from the DRC, thus increasing the incentive for DRC coltan to be re-exported as Rwanda's. Rwanda is also alleged to be trading in fraudulently exported gold and diamonds from the DRC. The country entered a high period of economic growth in 2006, and the following year managed to register 8% economic growth, a record it has sustained since, turning it into one of the fastest-growing economies in Africa. This sustained economic growth has succeeded in reducing poverty and also reducing fertility rates, with growth between 2006 and 2011 reducing the percentage of the country's population living in poverty from 57% to 45%.The country's infrastructure has also grown rapidly, with connections to electricity going from 91,000 in 2006 to 215,000 in 2011. Existing foreign investment is concentrated in commercial establishments, mining, tea, coffee, and tourism. Minimum wage and social security regulations are in force, and the four prewar independent trade unions are back in operation. The largest union, CESTRAR, was created as an organ of the government but became fully independent with the political reforms introduced by the 1991 constitution. As security in Rwanda improves, the country's nascent tourism sector shows great potential to expand as a source of foreign exchange. In 2016, Rwanda was ranked 42nd and second best country in Africa to do business in the Mara Foundation-The Ashish J Thakkar Global Entrepreneurship Index report. However, a recent research in the UK-based political science journal, Review of African Political Economy, indicates that economic growth may be slower than what official figures suggest. Researchers stated that average consumption per household closely followed growth in GDP per capita from 2000 to 2005, but diverged afterwards when average consumption per household stagnated despite huge improvements in GDP per capita from 2005 to 2013.