| Value | Category | Cases | |
|---|---|---|---|
| 1 | more than once a year | 1213 |
11.2%
|
| 2 | every year | 7052 |
65%
|
| 3 | every three years | 650 |
6%
|
| 4 | has done only once | 954 |
8.8%
|
| 6 | other | 978 |
9%
|
| Sysmiss | 2068 |