Year	Percent
1990	60.82
1991	60.95
1992	61.05
1993	61.09
1994	61.06
1995	61.31
1996	61.51
1997	61.89
1998	62.31
1999	62.8
2000	63.37
2001	63.89
2002	64.45
2003	65.02
2004	65.56
2005	66.06
2006	66.01
2007	65.92
2008	65.82
2009	65.72
2010	65.63
2011	65.62
2012	65.63
2013	65.66
2014	66.28
2015	66.59
2016	67.52
2017	67.19
2018	67.46
2019	67.71