Year	Percent
1990	56.96
1991	57.23
1992	57.13
1993	57.21
1994	57.56
1995	57.67
1996	57.91
1997	58.02
1998	58.21
1999	58.4
2000	58.34
2001	58.48
2002	58.64
2003	58.8
2004	58.95
2005	59.37
2006	59.79
2007	60.19
2008	60.6
2009	61.01
2010	61.43
2011	61.86
2012	62.28
2013	62.71
2014	63.13
2015	63.26
2016	63.3
2017	63.34
2018	63.41
2019	63.51