Year	Percent
1983	51.23
1984	52.2
1985	52.58
1986	53.2
1987	53.36
1988	54.03
1989	54.65
1990	54.87
1991	55.22
1992	56.8
1993	57.46
1994	60.34
1995	60.56
1996	62.27
1997	63.47
1998	63.95
1999	64.01
2000	63.92
2001	64.83
2002	65.39
2003	65.58
2004	68.25
2005	67.15
2006	66.59
2007	67.15
2008	68.51
2009	69.71
2010	69.88
2011	69.04
2012	69.24
2013	69.52
2014	69.41
2015	69.7
2016	70.09
2017	71.15