| Value | Category |
|---|---|
| 01 | Less than 1 month |
| 02 | From 1 to less than 4 months |
| 03 | From 4 month to less than 7 months |
| 04 | From 7 months to less than 1 year |
| 05 | From 1 to less than 2 years |
| 06 | From 2 years to less than 3 years |
| 07 | From 3 or more years |
| 98 | Do not know |
| 99 | NIU (not in universe) |