Year	Percent
1990	64.43
1991	63.96
1992	63.46
1993	60.21
1994	62.35
1995	62.37
1996	61.58
1997	60.42
1998	60.84
1999	60.4
2000	58.17
2001	58.15
2002	58.5
2003	57.82
2004	56.96
2005	57.43
2006	56.68
2007	56.83
2008	57.63
2009	58.87
2010	60.59
2011	61.84
2012	62.41
2013	63.57
2014	64.05
2015	65.15
2016	66.23
2017	67.31
2018	67.77
2019	67.91