| Value | Category |
|---|---|
| -9 | Don't know |
| -8 | Refused |
| -5 | Not applicable |
| -3 | Missing |
| 1 | Less than 3 months |
| 2 | 3 months - less than 6 months |
| 3 | 6 months - less than 9 months |
| 4 | 9 months - less than 1 year |
| 5 | 1 year - less than three years |
| 6 | 3 years - less than 5 years |
| 7 | More than 5 years |
| Sysmiss |