Year	Percent
1990	45.62
1991	45.68
1992	45.53
1993	46.14
1994	47.72
1995	49.98
1996	52.18
1997	57.83
1998	59.18
1999	55.99
2000	56.27
2001	57.78
2002	58.5
2003	58.97
2004	60.37
2005	60.3
2006	60.87
2007	61.98
2008	62.5
2009	64.11
2010	64.51
2011	64.86
2012	64.91
2013	65.28
2014	65.76
2015	66.11
2016	66.34
2017	67.13