| Value | Category |
|---|---|
| -9 | Don't know |
| -8 | Refused |
| -5 | Not applicable |
| -3 | Missing |
| 1 | In the last 30 days |
| 2 | One to five months ago |
| 3 | Six to twelve months ago |
| 4 | More than one and less two years ago |
| 5 | Two to four years ago |
| 6 | Five to ten years ago |
| 7 | More than ten years ago |
| 8 | Never |
| Sysmiss |