| Value | Category | Cases | |
|---|---|---|---|
| 1 | more than once a year | 2771 |
11.2%
|
| 2 | every year | 15877 |
64.2%
|
| 3 | every three years | 1504 |
6.1%
|
| 4 | has done only once | 2366 |
9.6%
|
| 6 | other | 2202 |
8.9%
|
| Sysmiss | 13998 |