Field entry, published 2026-11-03T00:00:00.000Z, updated 2026-11-03T00:00:00.000Z. Group: The four levels of ISCO-08

What is a sub-major group?

A sub-major group is the second tier in ISCO-08, a two digit division that splits a major group into smaller families of work. There are 43 sub-major groups across the whole classification, so a typical major group divides into about four sub-major groups, although the real split varies by branch. Each sub-major group belongs to exactly one major group, and its first digit is the digit of that parent. A reader who knows the two digit code therefore already knows the broader family, because the opening digit carries that information with it.

How does a sub-major group differ from its parent?

The difference is one of scope, not of kind. A major group says, in effect, here is a broad field. A sub-major group says, here is a recognisable part of that field, separated from the other parts because its work draws on a different specialisation or a different cluster of tasks. The split is still broad: a sub-major group is far from a single occupation. To take the one published example used across this cluster, 22 Health Professionals sits inside 2 Professionals. Health work is a distinct part of the professional family, but it still covers many different professional occupations, and it needs further division before any detailed occupation comes into view.

Why stop at two digits instead of going straight to detail?

An intermediate level is useful because many questions sit between the very broad and the very detailed. A comparison of health professional work with other professional work, for instance, is clearer at the sub-major level than at the major level, where health work would be merged with every other professional family, and clearer than at the unit level, where dozens of detailed groups would fragment the picture. Sub-major groups give analysts and readers a middle view: detailed enough to show real differences between fields, yet compact enough, with only 43 groups in total, to be read as a whole. That middle view is also a practical aid to navigation. When you are unsure where a detailed group belongs, finding its sub-major group first narrows the search to one branch.

What sits below a sub-major group?

Below each sub-major group sit minor groups, the three digit level, and below those sit unit groups, the four digit level. The sub-major group therefore acts as a gateway: everything beneath it shares its two digit opening, and everything outside it starts with a different two digit combination. That gateway role makes the sub-major level a good checkpoint when reading a code. If the first two digits look unfamiliar, the rest of the code cannot be understood properly until that two digit family is understood. Conversely, once the sub-major family is clear, the remaining digits can be read as successive refinements inside a known field rather than as an opaque string.

What mistakes happen at this level?

One mistake is to treat a sub-major group as if it were a detailed occupation, which overreads a still broad label. Another mistake is to assume that sub-major groups divide their parent evenly. They do not. One major group may split into two sub-major groups, while another splits into six or more, depending on how varied the work inside it is. A third mistake is to guess the meaning of a two digit code from its second digit alone. The second digit gains meaning only together with the first, because the same second digit can appear under different major groups with entirely different meanings. Always read the two digits as a pair, inside their parent family.

How can you use the sub-major level well?

Use it as a sorting shelf before you reach for detail. When a question concerns a field rather than a single occupation, stay at this level and compare sub-major groups with each other. When a question concerns detail, pass through this level deliberately: name the major group, name the sub-major group inside it, and only then move to minor and unit groups. That deliberate passage through the middle tier reduces the chance of landing in the wrong branch, because an error made at the sub-major step is easier to spot than an error made after jumping straight to a four digit code. The middle tier is, in short, where broad understanding turns into a reliable route toward detail.

Sources checked

1. ILO ISCO-08

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