Year	Percent
1991	57.89
1992	57.65
1993	57.54
1994	57.33
1995	57.24
1996	57.01
1997	56.51
1998	56.01
1999	55.52
2000	55.09
2001	54.96
2002	54.87
2003	54.82
2004	54.8
2005	54.76
2006	55.66
2007	56.53
2008	57.34
2009	58
2010	58.79
2011	59.72
2012	58.69
2013	57.66
2014	56.64
2015	56.22
2016	55.64
2017	55.46
2018	55.3
2019	55.19
2020	53.45