Year	Percent
1990	60.46
1991	60.81
1992	58.96
1993	58.58
1994	58.2
1995	57.94
1996	58.25
1997	58.43
1998	59.02
1999	59.49
2000	59.81
2001	60.25
2002	61.05
2003	61.82
2004	63.02
2005	62.56
2006	62.61
2007	62.37
2008	62.84
2009	62.19
2010	62.02
2011	62.15
2012	63.57
2013	63.38
2014	63.95
2015	64.07
2016	64.98
2017	65.49
2018	65.71
2019	65.82