Year	Percent
1975	73.99551
1976	71.81472
1977	67.98171
1978	68.0588
1979	71.35555
1980	72.66361
1981	68.36331
1982	63.15205
1983	61.40418
1984	62.81071
1985	61.25215
1986	52.15437
1987	54.6811
1988	53.01424
1989	55.07693
1990	58.90235
1991	46.7783
1992	55.29802
1993	51.47992
1994	46.26038
1995	45.54517
1996	46.367
1997	45.42841
1998	40.02353
1999	42.02066
2000	48.51701
2001	49.67634
2002	47.54575
2003	49.12101
2004	51.67835
2005	55.64361
2006	57.90311
2007	54.84023
2008	58.01798
2009	52.04496
2010	52.5496
2011	58.05116
2012	57.46363
2013	55.02007
2014	52.77811
2015	43.90903
2016	41.44868
2017	43.59679