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    The conceptual approach adopted for ISCO-88 resulted in a pyramid whose hierarchical structure consists of ten major groups at the top level of aggregation, subdivided into 28 sub-major groups, 116 minor groups, and 390 unit groups.

    As can be seen from the above table, out of the ten major groups, eight have been linked to the four ISCO skill levels - which, as mentioned earlier, were given operational definitions by reference to the educational categories and levels of the International Standard Classification of Education. The concept of skill level was not applied in the case of Major group 1, Legislators, senior officials and managers, and Major group 0, Armed forces. The reason for this was that, based on information from national sources, skills for executing tasks and duties of occupations belonging to each of these two major groups vary to such an extent that it would be impossible to link them with any of the four broad ISCO-88 skill levels.

    Further sub-divisions of ISCO-88 occupational groups, providing successively finer detail, were carried out on the basis of skill specialisation, defined by reference to the field of knowledge required, the tools and machinery used, the materials worked on or with, as well as the kinds of goods and services produced.

    The 28 sub-major groups, at the second ISCO-88 level of aggregation, represent an innovation in the sense that all of the preceding international occupational classifications have had a substantial numerical gap in the number of groups at their first and second levels of aggregation. For instance, in the case of ISCO-68 there were eight groups at the first level of aggregation followed by 83 groups at the second level. This presented an imbalance in the number of groups needed, on the one hand, for the presentation of the occupational structure in broad terms and for cross-classifying with variables such as industry or detailed age groups and, on the other hand, for presenting the occupational structure without cross-classifying, or when cross-classifying with variables such as sex or broad age groups.

    The 390 unit groups, representing the most detailed level of the ISCO-88 structure, in most cases consist of more than one occupation. In national circumstances, the number and delineation between occupations will, to a large extent, depend on the size of the economy and the level of economic development, the level and type of technology, work organisation and historical circumstances. For this reason detailed descriptions of the occupations belonging to each of the 390 unit groups have not been developed for ISCO-88. However, a selection is being made among the 1,506 detailed occupational descriptions which were included in ISCO-68. Those found to be still relevant will be published in a companion volume to ISCO-88.

    For each of the groups at the four levels of aggregation of ISCO-88 a code number, a title and a brief description of the content is provided. In the case of the unit groups, the main tasks of the occupations belonging to each of them are briefly described and some of the relevant occupational titles are listed as examples. In most cases examples are also given of the occupations which, although related in some way to those belonging to the unit group in question, are classified elsewhere. This has been done in order to clarify possible ambiguities and to highlight the ISCO-88 conceptual approach and characteristics of its structure.

    Detailed descriptions of the occupational groups at the four levels of aggregation are followed by the ISCO-88 index of occupational titles. Three separate listings of the index are provided. The first is according to ISCO-88 numerical order, the second by ISCO-68 numerical order, and the third is an alphabetical list of occupational titles. The index reflects the results of a recoding and recasting of the ISCO-68 "Expanded alphabetical list of titles". For further details the reader is referred to the " Notes on the ISCO-88 index of occupational titles" which precede the index.

    While revising the index, every effort was made to take into consideration the conceptual and structural differences between the two classifications, and, where possible, to make appropriate modifications, including some new index entries. However, some of the shortcomings of the ISCO-68 index - such as unevenness of detail when naming specialisations relating to a given generic occupational title - have been carried over to the present index. The user should bear in mind that the main aim of the present index is to indicate the content of each group within the ISCO-88 structure, and that the index makes no claim to being exhaustive. The Bureau of Statistics of the ILO intends, by using the latest national sources of occupational titles, to compile an extended and updated version of the ISCO-88 index for later publication. It is hoped that any shortcomings in the present index will be dealt with satisfactorily in the later version.

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 Updated 15 September 2004, by VA.