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Understanding ISCO88 (COM)

SCO88 (COM) is the European Union variant of the International Standard Classification of Occupations. It is a harmonised variable that is included in the main comparative datasets covering the European Research Area: the Labour Force Survey, the European Social Survey and EU-SILC.

Individual countries code to their own national classifications. In the majority of cases, these are based very closely on ISCO. In a number of other cases, for instance Great Britain, Ireland, France and Germany, there is a more distinct national classification that can be ‘mapped’ directly onto ISCO through a conversion table or ‘crosswalk’.

ISCO organises occupations into a hierarchical framework. At the lowest level is the unit of classification – a job – which is defined as a set of tasks or duties designed to be executed by one person. Jobs are then grouped into occupations according to the degree of similarity in their constituent tasks and duties (Elias and Birch 1994).

ISCO has four nested tiers reflected in the numbering of the occupational codes:

  • Major groups – top-level, broad definitions of occupation, providing the first digit of the ISCO code
  • Sub-major groups – second-level definition of occupation, providing first two digits
  • Minor groups – third-level definition, providing the first three digits
  • Unit groups – lowest, most detailed definition of occupation, providing the complete four-figure ISCO code

Table 2: Hierarchical Structure of ISCO88 (COM)

A comprehensive guide to ISCO88 (COM) is available.

Datasets usually contain ISCO coded to fewer than four digits. This can happen for a number of reasons: respondents may supply insufficient information; codes may be aggregated to comply with rules on confidentiality; crosswalks may not allow such precise coding. ESeC can be created using ISCO based on either three or two digits.

For example an interviewer may simply know that the person in question is a ‘corporate manager’ (sub major group 12). Where information is aggregated in this way there can be a problem if the minor groups within group 12 have different class positions. In this case the modal class for ISCO 12 employees is used. The SPSS syntax deals with these instances automatically, based on frequency distributions from pooled aggregate data in rounds 1 and 2 of the European Social Survey (see Appendix 8). If analysts are comparing only a small group of countries, or doing a single nation study, they might be advised to calculate modal values for each country.

In the process described above, some minor groups in ISCO will move between ESeC classes depending upon their numerical significance within a larger aggregate group. This in turn will lead to different distributions for the ESeC schema. A full list of distributions for ESeC based on differing levels of information is shown in Appendix 2.

In addition to the overall ‘shape’ of the ESeC distribution, analysts will be interested in two pieces of information: firstly the overall ‘level of agreement’ between derivations, that is to say the number of cases that stay in the same class; secondly the proportion of cases that move between each individual class and the others. Mutual exchange between any two classes will cancel each other out and so may not be apparent when comparing distributions.

The overall agreement between ESeC based on three digit and two digit ISCO is 86%. The correspondences between classes are shown below. Short range moves between adjacent classes are unlikely to cause problems for analysts; of more concern will be exchanges of cases between classes with different employment contracts, for instance 2 and 6 or 3 and 7.

Table 3: Correspondence Between 3 Digit and 2 Digit (‘Full’ Versions)