| Value | Category | Cases | |
|---|---|---|---|
| 0 | Never absent | 1072 |
49.2%
|
| 1 | Less than 3 months | 883 |
40.5%
|
| 2 | 3-6 months | 166 |
7.6%
|
| 3 | 6-9 months | 19 |
0.9%
|
| 4 | More than 9 months | 38 |
1.7%
|
| Sysmiss | 4983 |