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    Comparisons of occupations among countries or regions demand that national occupational statistics be converted to international standards. This is usually achieved by mapping the national occupational categories into a common international classification system, ISCO-88. International comparability of occupational statistics can also be achieved by using the international classification system to recode the original responses elicited by the occupational questions in censuses or other surveys. However, this latter method normally cannot be used because of the high costs 'Involved.

    Mapping one classification into another is equivalent to coding each group in the first classification to the most appropriate group in the other The validity of the mapping is in inverse proportion to the aggregated level at which the mapping is done. That is why it is recommended that mapping should be carried out at the lowest level of aggregation of each of the two classifications, i.e. national occupational classification (NOC) and ISCO-88.

    In the process of mapping, the three following situations are those most frequently encountered:

    (a) The NOC group,at the lowest level of aggregation, belongs unambiguously to one of the ISCO-88 unit groups. This is, of course, the simplest situation and, if the NOC, both conceptually and structurally, has a base similar to ISCO-88, it is likely to be the most usual situation.

    (b) The NOC group, at the lowest level of aggregation, differs in occupational content from the most relevant ISCO-88 unit group, but the difference in the content does not prevent the NOC group from being validly mapped into an ISCO-88 group at one of the higher levels of aggregation. For example: NOC classifies glass engravers and etchers together with glass and ceramics decorative painters in the same lowest level aggregation group, while ISCO-88 classifies these occupations in two unit groups, but in both classifications subsequent aggregation of these occupations 'is carried out in the same manner

    (c) The way of grouping certain occupations is different in NOC from that applied in ISCO-88, and, as a result, an existing NOC group cannot validly be mapped into any of the ISCO-88 groups. For example: at the lowest aggregation level, NOC classifies farmers, farm managers and farm labourers in one single group, while ISCO-88 classifies these occupations in three separate unit groups belonging to three different minor, sub-major and major groups.

    If internationally available occupational statistics have to be produced at the minor group aggregation level of ISCO-88, or any of the higher ones, then no problem arises in the situation described under (b) above. If the information has to be produced at the level corresponding to ISCO-88 unit groups, in that case, as well as in the situation described under (c) above, the following rules should be applied in order of priority as they are described:

    The numerical dominance rule, according to which, on the basis of the additional information available from economic and other statistics, or from sectoral experts, estimates or judgement should be made concerning the relative importance of the occupations classified in the NOC group. If approximately 80 per cent or more of the Jobs classified in the NOC group belong to a particular ISCO-88 group, then the whole NOC group should be classified in this ISCO-88 group.

    The skill level rule, according to which the occupational mix of the NOC group should be analysed on the basis of the ISCO-88 skill-level concept. The mapping into an ISCO-88 group should then be carried out on the basis of the occupations found to be the most skilled.

    The production rule, according to which, for the purposes of mapping into ISCO-88, in the occupational mix of a NOC group production occupations will have priority over sales or managerial occupations.

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 Updated 15 September 2004, by VA.