Year	Percent
1990	55.96
1991	56.74
1992	57.59
1993	58.5
1994	59.48
1995	60.54
1996	61.55
1997	62.63
1998	63.78
1999	64.98
2000	66.2
2001	66.47
2002	66.79
2003	67.13
2004	67.48
2005	67.8
2006	67.92
2007	68.07
2008	68.26
2009	68.57
2010	70.21
2011	72.07
2012	73.92
2013	75.7
2014	77.4
2015	76.99
2016	76.23
2017	76.78
2018	77.27
2019	77.62