The sub-index contains two indicators: adult literacy and the combined gross enrolment ratio. Adult literacy is measured as “the percentage of people aged 15 and above who can, with understanding, both read and write a short, simple statement on everyday life” (UNDP 1990: 182). The combined gross primary, secondary, and tertiary enrolment ratio is the average of the ratios of the number of students enrolled in a given level of education as a percentage of the population in the appropriate age group. The literacy indicator counts for two-thirds of the sub index score since the United Nations believes that “literacy is the first step in learning and knowledge-building” and deserves the greater emphasis (UNDP 1990: 12); the combined gross enrolment ratio counts for one-third. The two indicators are combined to arrive at the score for the sub-index.