| Value | Category | Cases | |
|---|---|---|---|
| 1 | Generally replacing every year | 14825 |
30.5%
|
| 2 | Replacing every alternate year | 15032 |
30.9%
|
| 3 | Replacing after three years | 9489 |
19.5%
|
| 4 | Replacing after four years or more | 9248 |
19%
|
| Sysmiss | 3176 |