Year	Percent
1970	55.30864
1971	55.09587
1972	55.73442
1973	56.00409
1974	56.05304
1975	55.08441
1976	55.1716
1977	55.16998
1978	54.74685
1979	52.85672
1980	51.61384
1981	51.19653
1982	51.4267
1983	50.8432
1984	49.42605
1985	49.44648
1986	53.91751
1987	54.97224
1988	57.01071
1989	56.48042
1990	56.35852
1991	57.40355
1992	57.7057
1993	57.65537
1994	56.7008
1995	55.33503
1996	53.56301
1997	53.2153
1998	56.55893
1999	55.15781
2000	49.86146
2001	51.53475
2002	53.45412
2003	53.8888
2004	52.38917
2005	49.82413
2006	48.1283
2007	50.33254
2008	48.61391
2009	53.69065
2010	52.75901
2011	51.11732
2012	51.69409
2013	52.62411
2014	54.02421
2015	56.53686
2016	58.07201
2017	56.77124