The primary sources of social indicators data are the data files and publications of specialized international agencies, such as Food and Agriculture Organization, International Labour Organisation, United Nations Educational, Scientific, and Cultural Organization, the UN Statistical Office, and World Health Organization. Supplementary sources are the Population Council, UN Research Institute for Social Development, and World Bank data files. Some demographic and labor force indicators are estimated by interpolating census observations.
The index of food production per capita shows the average annual quantity of food produced per capita. For this index, food is defined as comprising nuts, fruits, pulses, cereals, vegetables, starchy roots, sugar beet, sugar cane, edible oils, livestock, and livestock products. Quantities of food are measured net of animal feed, seeds for use in agriculture, and food lost in processing and distribution.
The data on primary school enrollment are estimates of children of all ages enrolled in primary school. Figures are expressed as the ratio of pupils to the population of children in the country's school age group. While many countries consider primary school age to be 6 to 11 years, others do not. For some countries with universal primary education, the gross enrollment ratios may exceed 100 percent because some pupils are younger or older than the country's standard primary school age.
The data on secondary school enrollment are calculated in the same manner, and the definition of secondary school age also differs among countries. It is most commonly considered to be 12 to 17 years.
Many indicators are based on census or household surveys, which occur infrequently. Thus some reported figures are interpolated or extrapolated estimates.