How do the ISIC Rev 5 and NACE Rev 2.1 structures compare?

ISIC Rev. 5 and NACE Rev. 2.1 match at the top of the hierarchy and differ below it. Both have 22 sections and 87 divisions. ISIC Rev. 5 has 258 groups and 463 classes. NACE Rev. 2.1 has 287 groups and 651 classes, as adopted. The match at the top is the basis for international comparison.

The difference below it is the European detail that NACE adds, as Eurostat states in its NACE background article: NACE is derived from ISIC, it is more detailed than ISIC, ISIC and NACE have exactly the same items at the highest levels, and NACE is typically more detailed at lower levels. A comparison that stops at the section or division level is a comparison on common ground. A comparison at group or class level needs a correspondence table.

What are the four levels, in each classification?

Both classifications use four levels, with the same identifier formats. A section is identified by one letter. A division is identified by two digits. A group is identified by three digits. A class is identified by four digits. The United Nations Statistics Division classification detail for ISIC Rev. 5 gives those formats and the item counts for each level. Eurostat gives the same formats for NACE, in the EUR-Lex summary and in its NACE background article, and the sample guide for this site records the NACE counts as adopted. The shared formats mean that a code string can look the same in both classifications while meaning different things at the lower levels, where NACE has more categories. A reader should therefore never assume that a four digit code in one classification is the same category as the same four digit code in the other, without checking the correspondence and the explanatory note for each.

Why do the group and class counts differ?

The counts differ because NACE adds detail that reflects European activities inadequately represented in ISIC, in the pattern Eurostat describes for earlier NACE revisions, and because NACE Rev. 2.1 introduces new concepts at all levels while maintaining the structure where no change was explicitly required. ISIC Rev. 5, for its part, recognises new industries and new activities that have emerged over the past 15 years, as the United Nations Statistics Division states. The two revisions were developed in parallel, with increased alignment as an aim, but they are separate classifications, adopted by separate bodies, on separate timetables. The difference in counts is therefore expected, and it is not a sign that one classification is wrong. It is a sign that the European classification carries more detail below the division level, and that the international classification carries the common frame above it. The table below shows the counts together, so that the match and the difference are visible at once.

Level	Identifier	ISIC Rev. 5	NACE Rev. 2.1
Section	One letter	22	22
Division	Two digits	87	87
Group	Three digits	258	287
Class	Four digits	463	651

The table is a count comparison only. It does not state that a given ISIC group corresponds to a given NACE group, and it does not state that the extra NACE groups and classes have no ISIC equivalent at a higher level. Those are correspondence questions, and they are answered in the correspondence tables, not in a count table.

How is a comparison made at the matching levels?

A comparison at section or division level is made by matching the letter or the two digits, and by checking that the titles match. The Central Statistics Office states that ISIC and NACE have exactly the same items at the highest levels, which supports a direct comparison at those levels, subject to checking the titles in the publications for the revisions in use. A comparison at those levels is an aggregate comparison: it compares totals for broad areas of activity, and it hides the detail below. That is appropriate for a broad comparison, such as comparing the size of manufacturing in two countries, where the detail below the division would add noise rather than information. It is not appropriate for a detailed comparison, such as comparing a specific service activity, where the NACE detail below the division is the point of the comparison, and the ISIC aggregate would hide it.

How is a comparison made below the matching levels?

A comparison below the division level is made through a correspondence table, and it must record the mapping type. Eurostat states on its correspondence tables page that two types of correspondence tables exist: tables between different versions of the same classification, and tables between two different classifications, which show the relationship between all positions of the two classifications involved. A NACE to ISIC table is a table of the second type. Where a NACE class has no direct ISIC equivalent at the same level, the table will show the relationship to the ISIC category above it, or to more than one ISIC category, and the mapping must be recorded as such. A one to many, many to one, or split mapping does not by itself pick a category for a specific unit, and it does not guarantee a one to one result. The explanatory note for each category remains the record of meaning, in both classifications.

What does the structure comparison not decide?

The structure comparison does not decide the code for any unit, and it does not decide tax, licensing, funding, collective agreement or social security questions. It describes two statistical classifications, their levels, and their counts. The entry for a specific business is confirmed, in the register classification version, with the national statistical institute or the business register holding the record. The meaning of a category in either classification is confirmed in the publication for that classification and revision.

Compare at section and division level on the common ground, use a correspondence table below it, and confirm a business entry with the institute or register that holds it. ”