The World Bank’s income thresholds are arbitrary breakpoints on a continuum.

Evidence

Figure 4.4 illustrates what can happen when you split the concept pair and consider each separately. The World Bank is dividing the continuum into parts that have conceptual names, such as poor (i.e., low income), middle income, and wealthy (i.e, high income). The standard data for this consist of GDP per capita, or more exactly in the case of the World Bank, GNI per capita (I use the term GDP per capita to refer to all similar or related measures of national income or production). I use the World Bank’s categorization for 2018 of countries into (1) low, (2) lower-middle, (3) higher-middle, and (4) high income to make the semantic transformation. The thresholds are 1,005 or less for “low,” 1,006–3,955 for “lower-middle income,” (3) 3,956–12,235 for “higher-middle income,” and (4) 12,236 and above for “high income” (World Bank, https://datahelpdesk.worldbank.org/knowledgebase/articles/378833). — Gary Goertz, Social Science Concepts and Measurement, 621

Categorization

• QUESTION: Worth chasing: the four-way split is wildly unequal in GDP range—why does no one contest the cut points?