Year	Percent
1968	46.67956
1969	46.13666
1970	46.06195
1971	50.27078
1972	44.26433
1973	51.79398
1974	70.37255
1975	68.07236
1976	70.782
1977	69.07924
1978	68.94684
1979	75.31073
1980	73.96755
1981	52.50068
1982	49.37907
1983	47.3449
1984	44.88932
1985	43.82086
1986	37.74911
1987	42.01818
1988	41.8563
1989	40.55194
1990	72.25233
1991	51.04943
1992	52.23207
1993	57.85826
1994	55.88644
1995	64.86536
1996	58.44651
1997	75.02028
1998	70.14709
1999	79.57411
2000	84.79598
2001	77.41958
2002	74.15786
2003	70.83823
2004	61.83506
2005	63.60843
2006	61.44419
2007	60.10771
2008	62.78886
2009	51.98979
2010	55.7935
2011	62.54803
2012	60.57699
2013	57.692
2014	56.539
2015	41.46
2016	37.3
2017	41.8