| Value | Category | Cases | |
|---|---|---|---|
| 1 | No bills are available | 1379 |
36.9%
|
| 2 | once a year | 44 |
1.2%
|
| 3 | once every six months | 20 |
0.5%
|
| 4 | once every two months | 1131 |
30.3%
|
| 5 | once per month | 1080 |
28.9%
|
| 6 | Others (specify) | 79 |
2.1%
|
| Sysmiss | 711 |