ISCO-08 Classification structure

ISCO-08 Classification structure and definitions

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What is an occupational classification?

An occupational classification is a tool for organising all jobs in an establishment, an industry or a country into a clearly defined set of groups according to the tasks and duties undertaken in the job.

It normally consists of two components:

  • The classification system itself, which gives the guidelines on how jobs are to be classified into the most detailed groups of the classification and how these detailed groups are to be further aggregated into broader groups. It includes the occupational titles and codes, and represents a value set for the variable occupation, a variable which describes the different tasks and duties of jobs.
  • A descriptive component, which usually consists of descriptions of the tasks and duties as well as other aspects of the jobs which belong to each of the defined groups, including goods and services produced, skill level and specialization, occupations included and excluded, entry restrictions, etc. These descriptions can be said to constitute a dictionary of occupations.

What are the basic principles of an occupational classification?

Any classification of occupations is based on principles for: classification unit(s), classification variable(s) and similarity criteria.

  • Classification unit(s)
    Occupational classifications generally classify jobs. Jobs can be: past, present or future jobs; paid employment jobs; self-employment jobs; jobs without incumbents (vacancies); etc.

Jobs which have the same set of main tasks and duties are aggregated (grouped together) into occupations. Occupations are grouped together into narrowly or broadly defined occupational groups on the basis of similarity in the type of work done, i.e. similarity in the tasks and duties performed. The units described in a dictionary of occupations are occupations and occupational groups.

  • The classification variable(s)

The classification variable in an occupational classification is usually the type of work done, or the tasks and duties performed.

  • The similarity criteria

The similarity criteria are fundamental to a classification of occupations. They determine the conceptual framework for the composition and location of categories and provide guidance on how to classify new or omitted occupations, how to establish similarity in the main attribute, and how to organize the occupations in the classification. They must relate to known attributes of an occupation and must be clearly and consistently defined and measured according to agreed methodology. Ideally, they should be determined by the use that will be and given to the classification. Thus, to be useful for job placement, human resource budgeting, education planning, skill should be the best criterion; but if the classification is to be useful for the analysis of social stratification or mobility, then occupational prestige would be a more suitable criterion.

Similarity criteria should meet the needs of any user. Unfortunately different users have different requirements with respect not only to the appropriate level of aggregation but also to the most appropriate similarity criteria.

For some users (for example, insurance companies) important criteria may be whether the work is carried out outdoors or indoors, or whether travelling is required or not. For other users, the social status of the work may be most important, or they may want to focus on the materials worked with, the goods and services produced or whether the work requires direct contact with clients and customers.

By deciding on the main similarity criteria to be used in the occupational classification, its developers implicitly or explicitly give priority to some users' needs over others. The implications of this for the overall use of the classification must therefore be carefully evaluated.

What are occupational classifications used for?

National occupational classifications and dictionaries are usually designed to serve several purposes. Although the detailed occupational descriptions and the classification structure must be seen as two parts of an integrated whole, different user areas have different degrees of interest in the various elements:

  • Detailed occupational descriptions are used by those who need to know about the tasks, duties and working conditions of jobs. They are mostly client oriented users (for example those responsible for job placement, vocational training and guidance, migration control, etc.). The occupational descriptions should be designed primarily to meet the needs of such users, but must also include the descriptive elements necessary for applying relevant aggregation schemes.
  • The classification structure, i.e. the grouping of the detailed occupations together in progressively more aggregate groups, should be designed mainly to facilitate the sorting of jobs and persons into groups, i.e. for the matching of job seekers and vacancies, or for statistical description and analysis of the labour market and the social and economic structure of society.

Depending on the purpose of the study, the variable occupation may be regarded as the main variable in the empirical analysis, or it may serve as a background variable. Used as a background variable, it may serve as a proxy for other variables such as socio economic groups or working conditions, or it may be used as one element in the construction of other variables, such as social class or socio economic status.

Who are the main users of occupational statistics?

  • Statistical services sort/classify jobs and persons into occupations to produce statistics on the occupational distribution of employed and unemployed persons, wages, working conditions, occupational injuries, etc, and statistics on the employed and unemployed persons, wages, working conditions, occupational injuries. etc. of particular occupations.
  • Migration authorities sort persons to make decisions about work permits or visas.
  • Employment services sort persons and jobs to match jobs seekers and vacancies.
  • Managers of enterprises/organisations use occupational statistics to sort jobs and persons to plan and decide on wage and other personnel policies, and monitor working conditions at the enterprise and in the context the industry and relevant labour markets.
  • Vocational counsellors use occupational information to guide school leavers and job seekers about types of work, training requirements, career prospects, working conditions, etc. of different types of jobs.
  • Vocational training specialists use occupational information as basis for planning and designing vocational training programmes.
  • Legislators and public sector administrators use occupational statistics in support of the formulation and implementation of economic and social policies and to monitor progress with respect to their application, including those covering manpower planning and the planning of education and vocational training.
  • Psychologists study the relationship between occupations and the personalities and interests of workers.
  • Epidemiologists use occupations in their study of work related differences in morbidity and mortality.
  • Sociologists use occupations as an important variable in the study of differences in life styles, behaviour and social positions.
  • Economists use occupation in the analysis of differences in the distribution of earnings and incomes over time and between groups, as well as in the analysis of imbalances of supply and demand in different labour markets.
  • The general public use occupational statistics to analyse, describe and learn about what is happening in their countries.

Methodological issues concerning the development, use, maintenance and revision of statistical classifications

The main tasks of the custodian of a national statistical classification are related to its development, use, maintenance and revision.
A statistical classification is a set of discrete values that can be assigned to specific variables which are to be measured in a statistical survey, or registered in administrative files to be used as a basis for statistics. Statistical classifications are not necessarily constructed by statisticians but by persons responsible for administering public policies (e.g. custom regulations, criminal legislation), providing public services (e.g. job placement, education, health services) or analysing social, economic or natural phenomena. When adopting and adapting such value-sets for their use in statistical inquiries, statisticians must understand whether and how the various methodological issues have been tackled and contribute to finding improved solutions to them where necessary and possible.

Developing a classification

When developing the classification, the custodian should consider:

Users' requirements:

  • How to determine who the main users are;
  • How to determine what the different users would like the classification to do;
  • How to balance the different users' requirements against each other or make a choice between them when they are contradictory.

    The main conceptual issues, given the users' requirements:

  • What are the (main) variable(s) for which the value-set is valid?

    Example: The variable to which ISCO-08 is applied is "main tasks and duties" of work performed, and not other aspects of work, such as exposure to hazardous substances or uncomfortable working conditions. Thus the variable "occupation" can be said to be defined as "the main tasks and duties of work performed".

  • What are the primary units for which we can measure the main variable(s)?

    Example: "jobs" are the primary units for ISCO-08. A "job" is defined as a set of tasks and duties (designed to be) performed by one person

  • What are the rules for linking other units to the primary units so that these other units can be assigned values of the classification variable?

    Example: "Persons" can only be assigned an "occupational group" through their link to a past, present or future job. They can only be given an "industry" code by being employed by an establishment.

  • What are the conceptual rules for identifying the same value of the variable?

    Example: For ISCO-08 the rule is "a set of jobs whose main tasks and duties are characterized by a high degree of similarity: they constitute an occupation", which is the most detailed element in the value-set for an occupational classification.

  • What are the similarity criteria used to define higher level categories (aggregated value-sets) in hierarchical classifications?
  • Example: In ISCO-08, the main similarity criteria are "skill level" and "skill specialisations" needed to carry out the tasks and duties of jobs.

  • The collection of information: how to collect the information which describes the defined categories and the dividing lines between them.

    Example: for an occupational classification one needs to collect information about the main tasks of jobs in the different occupations for the whole range of work situations that can be found in establishments of different size and in different industries. If one wants to be able to apply different similarity criteria to define alternative aggregated value sets, then all the corresponding information must be collected.

Using the classification

Using a classification involves the recording of the appropriate value of the value set for a particular unit. When using the classification, the following issues are important for statistical surveys and administrative records:

Respondent, interviewer or expert coding:

  • With respondent coding the respondent is presented with a value-set and asked to indicate the value which best applies to him/her.
  • With interviewer coding it is the interviewer who determines the correct value on the basis of the respondent's information.
  • With expert coding, the respondent or interviewer writes down the information from which someone (the expert) later will determine the correct value.

    What question(s) to ask, which depends on the choice of coder:

  • Respondents who code, i.e. select a category, need to be told on what basis they should choose one of the possible categories.
  • Interviewers who code need to get the information relevant for coding by themselves or by experts.

    Example: With interviewer or expert coding, the best basis for determining the occupational code is to ask questions about the occupational title as well as about the main tasks and duties.

    Instructions about which response elements

    to use and how to use them ensure that interviewers record the most important response elements and that coders use them consistently. The coding process should correctly retain as much of the information provided by respondents as possible.

    Example: The ILO recommends that when coding "occupation" one should code to the most detailed level in the classification that is supported by the information provided. Title, task etc. should be used according to clearly specified rules.

How to develop appropriate coding tools?

This concerns the development of coding indexes reflecting the type of responses given, as well as with coding rules. The development of automated or computer-assisted coding procedures should reflect the rules to be used for accurate and effective coding.

Quality control procedures

Quality control procesures re needed to monitor the quality of the coding process and to provide feedback both to coders and those responsible for the classification itself and the coding tools.

Maintaining the classification

Maintaining a classification involves:

  • the correction of errors made in the construction of the classification (value set) and associated coding tools; and
  • up-dating of the descriptions of the value-sets, dividing lines between groups and coding tools of the classification when previously unknown or genuinely new types of primary units emerge or are discovered, or as new information is obtained about existing types.

Maintaining a classification should be an ongoing activity of those responsible for the classification, to be combined with training and back-stopping for users of the classification or of the resulting statistics. The main methodological issues are:

  • How to best organize maintenance activities.
  • Criteria to identify "significant" effects of maintenance activities on comparability of data;
  • Development of methods to correct and smooth statistics for the effects of maintenance.

Revising the classification

Revising a classification involves a complete review of users' needs as well as the conceptual basis and the users' tools. Such reviews should only be undertaken at long intervals (10-15 years) or if there is compelling evidence that revisions are necessary. Such evidence may come from national users or from international developments.

The activities involved in revising a classification are essentially the same as those needed to develop it. However, additional methodological issues involved are:

  • How to determine whether a revision is needed.
  • How to determine whether new solutions are better than current practices.
  • How to implement a revised classification in on-going statistical programmes, given the need for comparability with past statistics.

More resources on ISCO-08

ISCO-08 Introductory and methodological notes

ISCO-08 Group definitions

ISCO-08 Complete publication

The history of ISCO

Distinctions between different occupational classes were introduced in population censuses undertaken in the early parts of the 19th century in several countries, but the identification of occupation and industry as different variables, each requiring its own classification, was only made towards the end of that century, as it became increasingly clear that the division of labour between firms and organizations in an industrial society was distinct from the division of labour between different jobs within the same firm.

The history of the development of the International Standard Classification of Occupations (ISCO) has always been closely connected with the work of the International Conference of Labour Statisticians (ICLS) which meets under the auspices of the International Labour Organization.

The need for an international standard classification of occupations was, in fact, discussed at the first ICLS in 1923, although this conference did not propose a specific grouping of occupations.

The first concrete step towards its establishment was the adoption, by the Seventh ICLS in 1949 of nine major groups termed the International Standard Classification of Occupations. The seventh ICLS proposed further development of this classification to more detailed level and identified basic principles to be followed in the collection and tabulation of occupational data, including that:

  • the basis of any classification of occupations should be the trade, profession or type of work performed by an individual, irrespective of the branch of economic activity to which he or she is attached or of his or her status in employment;
  • proprietors or owners who mainly perform the same work as that performed by employees in their own or in a similar enterprise should be allocated to the same group to which the employees are allocated.

In 1952, the ILO published the International Classification of Occupations for Migration and Employment Placement (ICOMEP), with descriptions of 1 727 occupations based on national reference materials sourced principally from 13 countries, and organized within the framework of the nine major groups adopted by the Seventh ICLS.

In 1954 the Eighth ICLS approved a list of minor groups which was subsequently submitted to the governments and to a group of experts for comments.

In 1957, the Ninth ICLS adopted the first complete version of the International Standard Classification of Occupations (ISCO-58) comprising a classification structure of 10 major groups, 73 minor groups, 201 unit groups, 1,345 occupations and an index of occupational titles. All groups at each level of the classification were given a unique code, title and description, drafted in consultation with the governments. It was published in 1958.

The Ninth ICLS also proposed a prompt revision of ISCO-58. In 1965, a working party examined proposals made on the basis of comments from about 80 countries and ten international organisations concerning the classification. This facilitated the development of a draft classification which was discussed, amended and adopted as ISCO-68 by the Eleventh ICLS in 1966. ISCO-68 consists of 8 major groups, 83 minor groups, 284 unit groups and 1506 occupational categories. It includes definitions for each of the 1881 groups describing the general functions of the occupations as well as the main tasks performed by the workers concerned. It includes an expanded alphabetical list of several thousand titles as well as a table of conversion from ISCO-58 to ISCO-68. The English and French versions were published in 1969 and the Spanish version in 1970.

The third edition of ISCO (ISCO-88) was adopted by the 14th ICLS in 1987 and approved by the ILO Governing Body in 1988. The major changes introduced were that

  • the underlying principles and concepts were made more explicit than in the previous versions;
  • skill level and skill specialization were identified as the main similarity criteria for arranging occupations into groups; and
  • the 10 major groups, 28 Sub-major groups, 116 minor groups and 390 unit groups in ISCO-88 provide much less detail than its predecessors, because experience had shown that it was very difficult to develop a comprehensive set of detailed categories that are applicable to all countries.

Early during the first decade of the 21st century, it became clear that there was a need to update ISCO-88. In December 2003 the 17th ICLS requested that the ILO complete work to update ISCO-88 by the end of 2007 so that the results could be taken into account in national preparations for the majority of population censuses to be undertaken in the 2010 round. The updated classification, ISCO-08 was adopted by a Meeting of Experts in Labour Statistics in December 2007.

Whilst it employs a similar conceptual model to that used for ISCO-88, and the 10 major groups were not changed in concept, ISCO-08 is slightly more detailed at its disaggregate levels and comprises 43 Sub-major groups, 131 minor groups and 425 unit groups. Like its predecessor, ISCO-08 provides descriptions for all of the categories identified at each of the four levels of its structure, and can be extended by defining detailed occupations if and when required for specific national or regional purposes.

Learn more about the ICLS: Reports, documents and other important material: