| Value | Category | Cases | |
|---|---|---|---|
| 1 | No bills are available | 341 |
14.8%
|
| 2 | once a year | 3 |
0.1%
|
| 3 | once every two months | 61 |
2.7%
|
| 4 | once per month | 1869 |
81.4%
|
| 5 | once per week | 7 |
0.3%
|
| 6 | Others (specify) | 16 |
0.7%
|
| Sysmiss | 2147 |