four skill levels ("armed forces" and "legislators, senior officials and managers," were not so categorized). For example, all occupations in the major group "clerks" are categorized at the second skill level, and all those in "elementary occupations" are at the first level. All descriptions are verbal, and no quantitative data are provided. Each major group, submajor group, and minor group is described by a general duty description and a list of tasks (usually no more than a brief paragraph in length). The lowest level "unit groups" also include names of "example occupations" and related occupations, in addition to the general duty and task list descriptions.

This development of this structure was "carried out in line with the recommendations and decisions of the Thirteenth and Fourteenth International Conferences of Labour Statisticians, held at the International Labour Office, Geneva, in 1982 and 1987" (International Labour Office, 1990:1). The underlying source data consist of population censuses, statistical surveys, and administrative records maintained at the national level.

The Organization for Economic Cooperation and Development (1997) recently reviewed the use of ISCO-88 in Europe and elsewhere around the world. It reached a number of conclusions:

• ISCO-88 has superseded ISCO-68 and has become the model for new national classifications in many countries, even those with previously existing systems.
• Levels of reliability of classifying occupations into ISCO categories remain fairly low, at 75 percent for the most detailed levels of categorization (about 350 categories).
• Aggregating to higher levels of categorization improves the correspondence of across-nation coding (aggregation to about the "submajor" level in ISCO-88 terms).
• International comparability of ISCO-88 results is improved through technical assistance to participating countries in the use of the system.

The Australian Standard Classification of Occupations (ASCO) uses the same concepts of skill level and skill specializa-