| Numbers | % | |
| Less than 1 year | 20 | 10.53 |
| 1 to 2 years | 40 | 21.05 |
| 2 to 4 years | 60 | 31.58 |
| 5 to 10 years | 40 | 21.05 |
| Unspecified | 30 | 15.79 |
| Total | 190 | 100 |