| 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 or four years ago | 
| 6 | Five to ten years ago | 
| 7 | More than ten years ago | 
| 8 | Never | 
| Sysmiss |