| Value | Category | Cases | |
|---|---|---|---|
| 1 | 1. Per month | 8 |
33.3%
|
| 2 | 2. Per semester | 3 |
12.5%
|
| 3 | 3. Per year | 13 |
54.2%
|
| 5 | 5. Others | 0 |
0%
|
| 6 | 6. None | 0 |
0%
|
| 9 | 9. Missing | 0 |
0%
|
| Sysmiss | 315 |