Countries fall into four wide human development categories, each of which has 47 countries: Very High Human Development, High Human Development, Medium Human Development and Low Human Development (46 countries in this category).
From 2007 to 2010, the first two categories was referred to as developed countries, and the last two are all grouped in developing countries. The original "high human development" category has been split into two as above in the report for 2007.
The country with the largest decrease in HDI since 1998 is Zimbabwe, falling from 0.514 in 1998 to 0.140 in 2010. The country with the largest decrease since 2009 is Cape Verde, which decreased by 0.170.
Over half of the world's population live in countries with "medium human development" (51%), while less than a fifth (18%) of the world's population are in countries that are in the "low human development" category. Countries with "high" to "very high" human development account for less than a third of the world's total population (30%).