Year Xi
Observed 
Observed 
1990
71.64
−0.8657
1995
74.22
−1.1371
2000
75.54
−1.2908
2005
76.65
−1.4323
2010
77.50
−1.5487
| Year Xi | Observed | Observed |
| 1990 | 71.64 | −0.8657 |
| 1995 | 74.22 | −1.1371 |
| 2000 | 75.54 | −1.2908 |
| 2005 | 76.65 | −1.4323 |
| 2010 | 77.50 | −1.5487 |