THE MARKET PYRAMID - Prahalad, C. K., & Lieberthal, K. (1998). The end of corporate imperialism. Harvard Business Review, 76(4), 68-79.
"Today managers take for granted that the biggest growth opportunities lie in the emerging markets - and that viable businesses can be built to serve people near 'the bottom of the pyramid.' That can be traced to ... [this article]. ... People living on $5,000 to $10,000 a year may not sound like lucrative customers, but they constitute a demographic of immense purchasing power for companies selling food, housing, or energy." (from HBR December 2011, p. 35)