Year	Percent
1970	66.38
1973	65.57
1974	62.09
1975	65.3
1976	64.3
1977	64.42
1978	63.27
1979	63.19
1980	62.59
1981	61.49
1982	62.15
1983	62.95
1984	62.14
1985	64.08
1986	64.46
1987	64.09
1988	63.67
1989	63.37
1990	61.68
1991	64.55
1992	65.05
1993	65.88
1994	66.96
1995	68.8
1996	69.57
1997	68.77
1998	69.61
1999	70.23
2000	65.49
2001	73.34
2002	74.02
2003	74.14
2004	75.17
2005	77.25
2006	76.66
2007	76.38
2008	76.24
2010	68.96
2011	79.21
2012	79.46
2013	80.13
2014	82.31
2015	82.67
2016	72.13