| Value | Category | Cases | |
|---|---|---|---|
| 1 | Within two years | 126 |
5.7%
|
| 2 | Within four years | 327 |
14.9%
|
| 3 | Within eight years | 385 |
17.5%
|
| 4 | More than eight years | 595 |
27.1%
|
| 5 | Never | 399 |
18.2%
|
| 9 | Don't know | 366 |
16.7%
|