When the first edition of this textbook was published in 1996, the World Bank defined "low-income country" as one with per capita income of less than $501. In 2003, when the third edition of Global Marketing appeared, "low income" was defined as $785 or less in per capita income. As shown in Table 2-4 of this chapter, $1,005 is the current "low income" threshold. The other stages of development have been revised upward in a similar manner. How do you explain the upward trend in the definition of income categories during the past 20 years?

Add the sources which are supporting your point of view.