| Value | Category | Cases | |
|---|---|---|---|
| 1 | Over one year | 78 |
57.4%
|
| 2 | Under one year | 55 |
40.4%
|
| 3 | I've never received negative results | 2 |
1.5%
|
| 4 | Choose not to answer | 1 |
0.7%
|
| Sysmiss | 421 |