Botswana has maintained one of the world's highest economic growth rates since independence in 1966, though growth fell below 5% in 2007-08, and turned sharply negative in 2009, with industry falling nearly 30%. Through fiscal discipline and sound management, Botswana transformed itself from one of the poorest countries in the world to a middle-income country with a per capita GDP of $13,100 in 2010. Two major investment services rank Botswana as the best credit risk in Africa. Diamond mining has fueled much of the expansion and currently accounts for more than one-third of GDP, 70-80% of export earnings, and about half of the government's revenues. Botswana's heavy reliance on a single luxury export was a critical factor in the sharp economic contraction of 2009. Tourism, financial services, subsistence farming, and cattle raising are other key sectors. Although unemployment was 7.5% in 2007 according to official reports, unofficial estimates place it closer to 40%. The prevalence of HIV/AIDS is second highest in the world and threatens Botswana's impressive economic gains. An expected leveling off in diamond mining production within the next two decades overshadows long-term prospects.