Year	Percent
1986	69.22
1987	70.44
1989	72.56
1990	71.49
1991	74.62
1992	75.59
1993	74.9
1994	73.35
1996	72.49
1997	71.56
1998	74.49
1999	75.46
2000	74.39
2001	73.31
2002	51.38
2003	50.68
2004	51.35
2005	51.11
2006	52.07
2007	54.28
2008	54.63
2009	55.04
2010	55.42
2011	55.24
2012	55.53
2013	55.56
2014	55.6
2015	55.17
2016	55.41
2017	56.65