Year	Percent
1980	38.65091
1981	47.09774
1982	50.63536
1983	52.95394
1984	54.7358
1985	49.74207
1986	50.43573
1987	54.42715
1988	50.67561
1989	50.1705
1990	54.01506
1991	56.47285
1992	59.11629
1993	60.25714
1994	55.99558
1995	58.33548
1996	59.66726
1997	59.78027
1998	58.7225
1999	58.97652
2000	54.84216
2001	54.05391
2002	51.87704
2003	56.63509
2004	55.84783
2005	54.51712
2006	50.69111
2007	52.95068
2008	51.49459
2009	55.80942
2010	57.22099
2011	57.62787
2012	55.88981
2013	57.26557
2014	57.90711
2015	59.10981
2016	58.08312
2017	58.41843