| Value | Category | Cases | |
|---|---|---|---|
| 1 | within two years | 204 |
10.4%
|
| 2 | within four years | 281 |
14.3%
|
| 3 | within eight years | 248 |
12.6%
|
| 4 | more than eight years | 328 |
16.7%
|
| 5 | never | 901 |
45.9%
|
| Sysmiss | 42 |