[Excerpt] This chapter is concerned with measuring how the extent of poverty changes in a country over time. 'Poverty', as the term is used here, denotes the inability of an individual or a family to command sufficient resources to satisfy basic needs. The poverty line is a constant real amount below which people are said to be poor. The extent of poverty in a country is then based on variables such as the number who are poor and the extent of their resource shortfall.
This chapter treats three topics: how poverty is defined, how much poverty there is, and how the extent of poverty has changed over time. The ideal would be to be able to use an internationally comparable poverty line (discussed in section 2) to construct a comprehensive poverty measure (defined in section 3) with which to determine how poverty has changed over time. But because the ideal is not now possible, the best we can do at present is to use country-specific poverty lines and non-comprehensive poverty measures. The evidence on this is summed up in section 4.