Year	Percent
1990	55.38
1991	55.79
1992	56.28
1993	56.74
1994	57.21
1995	57.55
1996	57.92
1997	58.05
1998	58.04
1999	58.1
2000	58.22
2001	58.29
2002	58.4
2003	58.57
2004	58.78
2005	59.73
2006	60.58
2007	61.89
2008	62.63
2009	64.02
2010	63.8
2011	63.87
2012	63.9
2013	63.89
2014	63.88
2015	63.95
2016	63.99
2017	64.12
2018	64.26
2019	64.29