Year	Percent
1971	98.31269
1972	96.44756
1973	94.93086
1974	94.28303
1975	95.63801
1976	97.06222
1977	98.59684
1978	101.24116
1979	101.66956
1980	98.72731
1981	97.13571
1982	95.51663
1983	96.09064
1984	98.22005
1985	100.33531
1986	105.15504
1987	95.68093
1988	96.60252
1989	94.54264
1992	96.73587
2004	96.77979
2005	94.09382
2006	96.36175
2007	94.54488
2010	92.43944
2011	90.66763
2012	94.11617
2013	92.50943
2014	92.88965
2015	94.62859