Table 1.
Properties of the Read Code Versions
| Concept | 4 Byte | Version 2 | Version 3 |
|---|---|---|---|
| Hierarchy representation | Code-dependent | Code-dependent | Link-based |
| Multiple parents | No | No | Yes |
| Hierarchy depth | 4 levels | 5 levels | Unlimited |
| Hierarchy relationships | Mixed | Mixed | Subtype |
| Meaningless identifiers | No | No | Yes |
| Compositionality | No | No | Constrained |
| Cross maps | BNF & ATC | OPCS4, ICD9, ICD10, BNF & ATC | OPCS4, ICD9, ICD10, BNF & ATC |
| Flexibility | No | No | Yes |
| Simplicity | Yes | Yes | No |
| Term identifiers | No | Yes | Yes |
| Semantic definitions | No | No | Yes |
| Number of concepts* | 40,927 | 88,995 | 187,598 |
| Number of terms* | 57,128 | 125,914 | 220,840 |
*
As at March 1997, including pharmacy.