Year	Percent
1968	62.04298
1969	61.11166
1970	58.35606
1971	65.3938
1972	67.34072
1973	69.74406
1974	83.12761
1975	71.84769
1976	70.55192
1977	67.04968
1978	60.21637
1979	64.87958
1980	71.49444
1981	70.75912
1982	59.79815
1983	49.421
1984	46.09876
1985	41.43862
1986	37.82063
1987	40.13978
1988	38.5527
1989	42.40348
1990	49.15624
1991	48.83531
1992	51.56569
1993	47.94338
1994	47.81222
1995	49.16691
1996	52.16139
1997	50.8188
1998	43.94791
1999	47.62675
2000	54.16668
2001	51.52505
2002	51.74224
2003	54.61857
2004	57.17497
2005	62.1148
2006	62.87713
2007	63.0347
2008	66.75665
2009	55.02005
2010	58.38421
2011	63.67637
2012	62.69116
2013	59.86246
2014	57.17584
2015	45.27245
2016	43.15745
2017	44.99629