Year	Percent
1990	60.17
1991	58.74
1992	59.58
1993	59.63
1994	60.48
1995	61.24
1996	62.21
1997	62.35
1998	63.8
1999	64.64
2000	64.9
2001	64.03
2002	64.82
2003	65.53
2004	66.99
2005	66.91
2006	67.2
2007	67.03
2008	66.96
2009	67.51
2010	67.78
2011	67.41
2012	67.69
2013	67.76
2014	67.62
2015	68.02
2016	68.32
2017	68.34
2018	68.39
2019	68.7