How is a correspondence table between NACE and ISIC read?

A correspondence table between NACE and ISIC is a table between two different classifications, which shows the relationship between all positions of the two classifications involved, in the words of Eurostat. Eurostat distinguishes two types of correspondence tables: tables between different versions of the same classification, and tables between two different classifications. A NACE to ISIC table is of the second type. It is read pair by pair, with the mapping type recorded for each pair, and it is never read as a list of one to one equivalents.

What does a correspondence table show?

A correspondence table shows, for each category in one classification, the category or categories in the other classification to which it relates. Eurostat states, for the NACE Rev. 2 to NACE Rev. 2.1 table, that the table describes, for each NACE Rev. 2 heading, how activities currently classified therein should be classified in NACE Rev. 2.1. The same descriptive pattern applies to a table between two classifications: for each heading in the source classification, the table shows the heading or headings in the target classification. The table also shows, by its structure, whether the relationship is one to one, one to many, many to one, or a split, and it can be used to represent special aggregations, such as the Main Industrial Groupings, as Eurostat notes. A table that is read without noting the mapping type has been read only in part, because the mapping type is the information that controls whether a comparison at that level is direct or aggregated.

What mapping types can appear?

Four mapping patterns can appear, and each must be recorded in the terms the table uses. A one to one mapping means one category in the source corresponds to one category in the target, at the level shown. A one to many mapping means one source category is split across two or more target categories, and the table alone does not allocate the split. A many to one mapping means two or more source categories fall in one target category, and the target is the comparable aggregate. A split, in the sense used for revision tables, means that activities move from one source class to more than one target class, and the explanatory notes for the target classes must be read to understand the division. Where no verified one to one mapping exists, compare at the aggregate level where categories match, or describe the split explicitly and cite the note for each target class. A mapping presented as a one to one guarantee, where the table shows a one to many or split pattern, misstates the table, and this guide does not present any mapping in those terms.

Mapping type	What it means	How a comparison is made
One to one	One source category to one target category	Direct comparison at that level, revisions named
One to many	One source category split across target categories	Compare at the aggregate, or describe the split
Many to one	Two or more source categories in one target category	Compare at the target aggregate level
Split	Activities move to more than one target class	Read the note for each target class, record the split

The table is a reading guide, not a correspondence table itself. It does not state that any named pair of categories has any named mapping type. The mapping type for a named pair is read from the correspondence table for the revisions in use, and it is recorded from that table, not from this guide.

How are the revisions named in a correspondence check?

The revisions are named for both classifications, in every check. A NACE to ISIC check must state whether it is NACE Rev. 2 to ISIC Rev. 4, NACE Rev. 2.1 to ISIC Rev. 5, or another pair, because the relationship between the classifications can change when either classification is revised. The United Nations Statistics Division states that ISIC Rev. 5 replaces Rev. 4, and Eurostat states that NACE Rev. 2.1 is the current European version, adopted by Commission Delegated Regulation (EU) 2023/137. A table for an earlier pair of revisions should not be used for a later pair without checking that the table has been updated for the later revisions. The version of the table itself should also be recorded, because correspondence tables are published, corrected, and republished, and a table consulted in one year may differ from the table consulted in another. The check record therefore names the source classification and revision, the target classification and revision, the table version or date, and the mapping type for the pair checked.

What is the role of the explanatory notes alongside the table?

The explanatory notes state what each category includes and excludes, and they are the record of meaning that the table alone does not provide. Eurostat states that its roll out work included publishing introductory guidelines that describe the overall logic of how activities are classified, and explanatory notes that give guidance for specific categories. The United Nations Statistics Division provides explanatory notes for ISIC Rev. 5 alongside its structure. A reader who consults the table without the notes can see that two categories are related, but cannot see why, or what activity sits on which side of the boundary. A reader who consults the notes without the table can see what each category covers, but cannot see how the categories relate across the two classifications. The check needs both, and the citation should name both, with the revisions for each.

What does a correspondence table not decide?

A correspondence table does not determine the code for any unit, and it does not decide tax, licensing, funding, collective agreement or social security questions. It describes the relationship between categories in two statistical classifications, for the purpose of comparing statistics. The national statistical institute or the business register holding the record confirms the entry for a specific business, using the classification version the register uses. The meaning of a category is confirmed in the explanatory notes for that classification and revision.

Record the two revisions, the table version, and the mapping type for each pair, read the note for each category, and confirm a business entry with the institute or register that holds it. ”