| 1983 | 1987 | 1991 | |
| Total | 100.0% | 100.0% | 100.0% |
| 1 year or less | 19.0% | 21.0% | 20.6% |
| 2 years | 9.6% | 10.0% | 9.9% |
| 3 years | 8.7% | 8.6% | 9.2% |
| 4 or 5 years | 13.8% | 10.5% | 11.8% |
| 6 to 9 years | 13.8% | 15.2% | 12.9% |
| 10 to 19 Years | 21.3% | 21.2% | 22.1% |
| 20 years or more | 14.0% | 13.5% | 13.5% |
| RETURN | |||