Year	Percent
1970	45.23004
1972	46.72234
1973	48.59982
1974	49.49123
1975	49.20911
1976	50.29703
1977	52.07669
1978	52.68585
1980	55.09198
1981	57.97542
1982	61.15394
1983	63.67713
1984	65.30003
1985	67.24463
1986	65.30839
1987	65.44992
1988	64.87301
1989	64.25126
1990	65.43528
1991	68.23556
1992	71.97216
1993	74.99598
1994	75.54744
1995	77.2392
1996	81.68596
1998	91.09729
1999	87.75852
2000	91.54211
2001	91.20835
2002	93.43129
2003	95.90019
2004	94.29864
2005	94.39782
2006	93.51928
2007	93.73179
2008	93.3338
2009	92.43647
2010	91.76142
2011	89.14726
2012	88.62471