| Value | Category | Cases | |
|---|---|---|---|
| 1 | more than once a year | 29 |
2.2%
|
| 2 | every year | 255 |
19.4%
|
| 3 | every two years | 87 |
6.6%
|
| 4 | every three years | 92 |
7%
|
| 5 | has done only once | 763 |
58%
|
| 6 | other | 89 |
6.8%
|
| Sysmiss | 34468 |