In the early days of the UN, poverty was measured in terms of the ability to meet a minimum number of calories or to have a minimum level of income to satisfy needs (income poverty). A "poverty line" defined this minimum level and the poor constituted the actual number of people whose incomes or calorie intake are less than this. A commonly used measure for purposes of international comparisons of income poverty is the $1 or $2 per day measure (purchasing power equivalent to $1 or $2 in the United States in 1993). There have been changes in thinking as to how to measure poverty with attempts at incorporating some of its various dimensions, as well as its circular connections that we talked about earlier. 

In the 1970s the International Labour Organization (ILO) broadened the focus, and poverty came to be seen as the inability to meet basic needs. In the 1980s and 90s, the concept underwent further change by considering non-monetary aspects such as isolation, powerlessness, vulnerability and lack of security, as well as an individual's capacity and capability to experience well being. 

Inspired by the work of Amartya Sen, a world famous economist who won the Nobel Prize for Economics in 1999, the United Nations Development Programme (UNDP) introduced measures for progress and for deprivation that focus on poverty from a human development perspective. It now views poverty as a denial of choices and opportunities for living a tolerable life. The human poverty index (HPI) constructed for each country provides a country-by-country picture of deprivation in terms of longevity, education and economic factors. Considering poverty in a different way leads to new observations. For example, an elevated level of the United States population experiences acute "human poverty" despite its high average income levels.