| 1 | primary education (ISCED97-1) |
| 2 | lower secondary (ISCED97-2) OR end of basic education |
| 3 | upper secondary or post-secondary non-tertiary (ISCED97 3 and 4) |
| 4 | university or post-graduate (ISCED97 5A and 5B) |
| 8 | other, only if none of the codes 0 to 4 applies |
| 9 | Unknown |