What is a correspondence table?

A correspondence table shows the relationship between categories in two classifications, or between two versions of the same classification, pair by pair. Eurostat states on its correspondence tables page that two types of correspondence tables exist: tables between different versions of the same classification, which describe the detailed changes that have taken place in the revision process, and tables between two different classifications, which show the relationship between all positions of the two classifications involved. A correspondence table is therefore a map, not a definition. The definition of a category is in its explanatory note.

The table shows how the categories on one side relate to the categories on the other, and it is read together with the notes, never instead of them.

What does a table between two versions show?

A table between two versions shows, for each heading in the old version, how the activities in it should be classified in the new version. Eurostat describes the NACE Rev. 2 to NACE Rev. 2.1 table as showing, for each Rev. 2 heading, where activities currently classified under it should be classified in Rev. 2.1. The table was made available to classification users on 1 August 2023 (FIXED, as stated in the implementing regulation recitals), along with the explanatory notes, so that users could assess the detailed content changes and compare the previous version with the updated version. A table between versions is read from the old heading to the new heading, and the mapping type for each pair is recorded. A table read in the reverse direction, from the new heading to the old, answers a different question, about where the activities in the new heading came from, and it should be labelled as a reverse reading, not as the same table read backwards without comment.

What does a table between two classifications show?

A table between two classifications shows the relationship between all positions of the two classifications involved, as Eurostat states. A NACE to ISIC table, for example, shows, for each NACE category, the ISIC category or categories to which it relates, and a NACE to CPA table shows the relationship between activity categories and product categories. A table between classifications is read pair by pair, with the mapping type recorded, and it is never read as a list of equivalents, because the two classifications classify different characteristics, or the same characteristic at different levels of detail. Where the target classification is more detailed, the table will show one source category relating to more than one target category. Where the source is more detailed, the table will show more than one source category relating to one target category. The mapping type is the information that controls whether a comparison at that level is direct or aggregated, and it must be recorded for each pair checked.

What mapping types appear in a table?

Four mapping patterns appear, and each must be recorded in the terms the table uses. A one to one mapping means one category on the source side corresponds to one category on the target side, at the level shown. A one to many mapping means one source category is split across two or more target categories. A many to one mapping means two or more source categories fall in one target category. 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 notes for the target classes must be read. Except where a one to one mapping has been verified, comparison belongs at the aggregate level where the categories match, or the split should be described explicitly, citing 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 site does not present any mapping in those terms.

Mapping type	Meaning	Comparison
One to one	One source to one target	Direct, at that level, revisions named
One to many	One source split across targets	Aggregate, or describe the split
Many to one	Many sources in one target	Aggregate at the target level
Split	Activities move to more than one target class	Read each target note, record the split

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

How is a table cited?

A table is cited by naming the two classifications or versions, the table version or date, and the mapping type for the pair checked. The Eurostat correspondence tables page links the tables between NACE Rev. 2 and NACE Rev. 2.1, and between Main Industrial Groupings and NACE Rev. 2.1, through ShowVoc, and the Central Statistics Office states that correspondence tables are available on ShowVoc, Eurostat’s web based metadata catalogue. A citation should state which table was consulted, in which form, and on what date, because tables are published, corrected, and republished, and a table consulted in one year may differ from the table consulted in another. A citation that states only that a correspondence exists, without naming the table and the mapping type, cannot be checked, and it should not be relied on for a comparison.

What does a table not decide?

A 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, for the purpose of comparing statistics. Where a specific business entry is confirmed is the national statistical institute or the business register holding the record. The meaning of a category is confirmed in the explanatory note for that category. The table is the bridge between versions and between classifications. The note is the meaning. The register is the entry.

Name the two sides and the table version, record the mapping type for each pair, and confirm a business entry with the institute or register that holds it.