| Value | Category | Cases | |
|---|---|---|---|
| 1 | within two years | 387 |
19.7%
|
| 2 | within four years | 427 |
21.8%
|
| 3 | within eight years | 292 |
14.9%
|
| 4 | more than eight years | 387 |
19.7%
|
| 5 | never | 468 |
23.9%
|
| Sysmiss | 43 |