| Average duration of recurrence | Frequency | Percent |
| Within two weeks | 2 | 0.2 |
| One month | 6 | 0.6 |
| Two months | 80 | 8.3 |
| Three months | 26 | 2.7 |
| Six months | 6 | 0.6 |
| One year | 20 | 2.1 |
| Two years | 19 | 2.0 |
| Missing | 810 | 83.6 |
| Total | 969 | 100 |