Literacy is measured operationally in terms of three domains, each encompassing a common set of skills relevant for diverse tasks:

• Prose literacy — the knowledge and skills needed to understand and use information from texts including editorials, news stories, poems and fiction.
• Document literacy — the knowledge and skills required to locate and use information contained in various formats, including job applications, payroll forms, transportation schedules, maps, tables and charts.
• Quantitative literacy — the knowledge and skills required to apply arithmetic operations, either alone or sequentially, to numbers embedded in printed materials, such as balancing an account, figuring out a tip, completing an order form or determining the amount of interest on a loan from an advertisement.

The IALS employed a sophisticated methodology developed and applied by the Educational Testing Service to measure literacy proficiency for each domain on a scale ranging from 0-500 points. Literacy ability in each domain is expressed by a score, defined as the point at which a person has an 80 percent chance of successful performance from among the set of tasks of varying difficulty included in the assessment.³ Five levels of literacy correspond to measured ranges of scores achieved. Level 1 indicates persons with very poor skills, where the individual may, for example, be unable to determine the correct amount of medicine to give a child from information printed on the package. Level 2 respondents can deal only with material that is simple, clearly laid out, and in which the tasks involved are not too complex. It denotes a weak level of skill, but more hidden than Level 1. It identifies people who can read, but test poorly. They may have developed coping skills to manage everyday literacy demands, but their low level of proficiency makes it difficult for them to face novel demands, such as learning new job skills. Performance at Levels 3, 4 and 5 requires the ability to integrate several sources of information and solve more complex problems.

Study Design

The data presented in this report were collected by the countries participating in successive cycles of data collection between 1994 and 1998, using nationally representative samples of the adult population aged 16-65. The fact that some countries collected data a few years earlier or later than others is thought not to affect the international comparability of the survey data because the literacy profiles of nations are quite stable and are normally expected to change only slowly with the passing of time.⁴

The survey was conducted in people's homes by experienced interviewers. The design used for IALS combined educational assessment techniques with methods of household survey research. Multiple quality control measures were implemented throughout the course of the study in order to ensure that high-quality data would be obtained. Annex B describes the measures taken to improve data quality and comparability and addresses specific issues concerning validity, reliability and comparability.

3. The RP-80 criterion is explained in Yamamoto, K. (1998), "Scaling and scale linking", pp. 161-178, in Murray, T.S., Kirsch, I.S., and Jenkins, L.B. (Eds.), op. cit.

4. The possibility that a nation succeeds in significantly altering its literacy profiles within the course of 4-5 years cannot be ruled out. Major educational reforms, for example, can influence the literacy profiles of specific sub-populations.