Year	Percent
1968	59.63905
1969	62.15192
1970	56.9799
1971	64.8385
1972	61.13508
1973	73.32336
1974	84.58956
1975	72.44832
1976	73.40088
1977	78.343
1978	76.19227
1979	78.57085
1980	84.62838
1981	84.18443
1982	78.12697
1983	65.84882
1984	59.55368
1985	49.18581
1986	45.18874
1987	50.53803
1988	52.30348
1989	51.95478
1990	58.22141
1991	58.14105
1992	61.25852
1993	53.09026
1994	48.79013
1995	54.50631
1996	55.76179
1997	53.90581
1998	46.89815
1999	48.7098
2000	56.89314
2001	53.92004
2002	55.24437
2003	62.53234
2004	67.00599
2005	73.12001
2006	74.58346
2007	77.78138
2008	82.45455
2009	67.0864
2010	67.77757
2011	73.93574
2012	73.9147
2013	72.86262
2014	68.25754
2015	57.8088
2016	50.19867
2017	51.03614