Year	Percent
1977	60.07126
1978	61.03509
1979	58.85953
1980	62.54044
1981	60.45429
1982	60.19409
1983	60.84783
1984	62.34556
1985	62.67337
1986	63.00535
1987	59.82106
1988	59.56575
1989	61.50711
1990	63.08244
1991	61.57827
1992	63.53587
1993	65.26229
1994	65.39274
1995	65.24579
1996	65.30132
1997	64.43882
1998	64.77591
1999	64.17127
2000	64.70566
2001	66.73827
2002	65.49961
2003	64.62227
2004	66.39738
2005	61.57675
2006	63.83823
2007	64.98693
2008	66.68331
2009	69.60314
2010	68.36618
2011	69.14541
2012	70.46613
2013	69.73974
2014	68.27706
2015	66.76277
2016	66.77939
2017	66.15958