In the early days of independence, with high revenues from copper exports, economists described Zambia as a "middle-income country" with the potential to become fully developed. Beginning in the 1970s, however, the Zambian economy suffered a major decline as a result of falling copper prices and rising oil prices. Per capita income dropped by 50 per cent between 1974 and 1994. The slow-down also highlighted what American political scientist John Harbeson described as a "massive and inefficient parastatal sector as well as the government's prevailing urban bias", and led to a fall in formal employment in Lusaka which continued for several decades. The lack of jobs decreased the level of rural-to-urban migration in Zambia, but the decline of the copper industry caused a large movement of people from the Copperbelt cities to Lusaka. This, and the natural population growth in the city's young population, gave Lusaka a population growth of around 4 per cent in the 1990s, exceeding the national average.