Year	Percent
1990	53.65
1991	53.86
1992	54.08
1993	54.29
1994	63.98
1995	64.23
1996	64.48
1997	64.73
1998	64.98
1999	65.23
2000	65.48
2001	65.73
2002	65.98
2003	66.23
2004	69.41
2005	69.67
2006	69.93
2007	70.19
2008	70.45
2009	70.71
2010	70.97
2011	71.23
2012	71.49
2013	71.75
2014	72.02
2015	72.28