What does same at the top, more detail below mean?

Same at the top, more detail below means that ISIC and NACE share the same categories at the highest levels of the hierarchy, while NACE adds more categories at the lower levels. Eurostat states in its NACE background article that NACE is derived from ISIC, in the sense that it is more detailed than ISIC, that ISIC and NACE have exactly the same items at the highest levels, and that NACE is typically more detailed at lower levels.

The Central Statistics Office states the same relationship: NACE is derived from ISIC, it is more detailed than ISIC, and ISIC and NACE have exactly the same items at the highest levels, but NACE is more detailed at lower levels. The phrase is a summary of the derivation, not a correspondence table, and it must be read with the revisions named.

What are the highest levels?

The highest levels are the section and the division. A section is the broadest grouping, identified by one letter, such as C for manufacturing in the earlier lettering, or J and K in the NACE Rev. 2.1 lettering for the split of the former information and communication section. A division narrows the section, and is identified by two digits. In ISIC Rev. 5 and NACE Rev. 2.1, both classifications have 22 sections and 87 divisions, as the United Nations Statistics Division detail and the adopted NACE structure show. The sameness at those levels means that a section total in one classification can be compared with the section total in the other, and a division total can be compared likewise, subject to checking the titles and the revisions. The sameness does not mean that every lower category matches, and it does not mean that the two classifications are interchangeable below the division.

What is the detail below?

The detail below is the group and the class. A group narrows the division, and is identified by three digits. A class is the most detailed level, and is identified by four digits. NACE Rev. 2.1 has 287 groups and 651 classes. ISIC Rev. 5 has 258 groups and 463 classes. The extra groups and classes in NACE are European detail: categories that reflect activities of particular importance in the European economy, or activities that need separate identification for European statistics, even where ISIC groups them together at a higher level. A reader who works at class level in NACE is therefore working at a level of detail that ISIC does not always provide, and a reader who aggregates a NACE class to its ISIC equivalent must use the correspondence table to find the ISIC category that contains it, rather than assuming a four digit match.

Why does the derivation run from ISIC to NACE, and not the other way?

The derivation runs from ISIC to NACE because ISIC is the international standard, adopted by the United Nations Statistical Commission, and NACE is the European implementation of it, adopted by the European Commission. The United Nations Statistics Division states that, since the adoption of the original ISIC in 1948 (FIXED), the majority of countries have used ISIC as their national classification or have developed national classifications derived from it. Eurostat states that the definitions and guidelines for NACE within the European Union are consistent with those published in the introduction to ISIC, in order to ensure international comparability. The direction matters for checking: a question about international comparability is answered by reference to ISIC, and a question about European detail is answered by reference to NACE. A question that confuses the direction, and treats a NACE detail as if it were an ISIC category, will misstate the international comparison.

Level	Shared?	What the sameness means
Section, one letter	Yes, same items at the highest levels	Section totals are comparable, titles checked
Division, two digits	Yes, same items at the highest levels	Division totals are comparable, titles checked
Group, three digits	No, NACE more detailed	Correspondence table needed
Class, four digits	No, NACE more detailed	Correspondence table and explanatory note needed

The table states the sameness level by level, rather than as a general claim. A general claim that NACE and ISIC are the same would be wrong below the division. A general claim that they are unrelated would be wrong at the top. The level by level statement is the accurate one, and it is the one a citation should use.

How is the phrase used in a citation?

The phrase is used in a citation with the revisions named, the levels named, and the source named. A citation should state that, for the revisions in use, ISIC and NACE have exactly the same items at the highest levels and NACE is more detailed at lower levels, citing Eurostat or the Central Statistics Office, and should name the revisions, such as ISIC Rev. 5 and NACE Rev. 2.1, or ISIC Rev. 4 and NACE Rev. 2, as the case requires. A citation that omits the revisions invites a reader to apply the statement to the wrong pair of revisions, where the counts and the titles may differ. A citation that omits the levels invites a reader to apply the sameness to the class level, where it does not hold.

What does the phrase not decide?

The phrase does not decide the code for any unit, and it does not decide any question about tax, licensing, funding, collective agreement or social security status. It describes the relationship between two statistical classifications. The holder of the record, the national statistical institute or the business register, is where a specific business entry is confirmed. The meaning of a category in either classification is confirmed in the publication for that classification and revision.

Name the revisions and the levels in every comparison, check the correspondence below the division, and confirm a business entry with the institute or register that holds it. ”