| Year | Mean (%) | Standard deviation (%) | Q1 (%) | Q2 (%) | Q3 (%) |
| 1991 | −6.54 | 38.62 | −33.78 | 0.00 | 18.32 |
| 1993 | 13.90 | 39.01 | −13.73 | 16.44 | 49.34 |
| 1997 | 15.66 | 38.00 | −13.55 | 14.25 | 51.68 |
| 2000 | 9.60 | 39.61 | −22.94 | 9.51 | 45.91 |
| 2004 | 18.24 | 30.29 | −2.48 | 17.75 | 41.68 |
| 2006 | 24.90 | 24.78 | 6.80 | 21.13 | 41.58 |