Year	Percent
1970	20.33779
1971	24.10537
1972	23.56849
1973	24.08416
1974	24.26219
1975	24.27287
1976	30.81174
1977	32.39766
1978	55.23953
1979	46.5153
1980	45.46264
1981	51.04722
1982	54.63168
1983	56.21414
1984	51.07103
1985	59.53987
1986	64.07031
1987	71.45616
1988	74.83852
1989	74.76017
1990	73.58721
1991	73.72689
1992	66.89568
1993	66.75742
1994	68.35699
1995	65.28632
1996	60.56699
1997	54.34093
1998	58.26386
1999	64.67862
2000	57.75335
2001	57.8881
2002	62.16036
2003	57.32626
2004	56.70456
2005	46.87441
2006	42.4995
2007	44.25797
2008	41.06458
2009	46.90673
2010	38.64685
2011	39.9055
2012	53.16221
2013	54.17658
2014	54.03571
2015	55.92635
2016	58.97036