| Value | Category |
|---|---|
| 1 | less than one week |
| 2 | 1 week or more but less than a month |
| 3 | 1 month or more but less than 3 months |
| 4 | 3 months or more but less than 6 months |
| 5 | 6 months or more but less than 1 year |
| 6 | 1 year or more but less than 2 years |
| 7 | 2 years or more |
| 8 | duration is unspecified |
| Sysmiss |