Year	Percent
1990	57.81
1991	58.05
1992	58.97
1993	59.7
1994	60.08
1995	60.14
1996	59.85
1997	58.04
1998	57.43
1999	56.96
2000	56.2
2001	56.26
2002	56.21
2003	57.21
2004	57.13
2005	57.04
2006	56.94
2007	56.81
2008	56.74
2009	56.68
2010	56.52
2011	56.33
2012	56.1
2013	55.8
2014	55.68
2015	55.54
2016	60.45
2017	60.24
2018	60.04
2019	59.94