Year	Percent
1991	58.11
1992	58.19
1993	57.73
1994	57.78
1995	57.46
1996	56.71
1997	56.51
1998	56.28
1999	56
2000	55.78
2001	54.46
2002	54.16
2003	54.27
2004	54.99
2005	55.31
2006	55.68
2007	56.01
2008	55.86
2009	54.47
2010	55.01
2011	55.7
2012	56.05
2013	56.14
2014	56.31
2015	56.53
2016	56.59
2017	56.78
2018	57
2019	57.19
2020	56.42