Year	Percent
1991	54.84
1992	54.63
1993	54.41
1994	54.37
1995	54.33
1996	54.28
1997	54.34
1998	54.38
1999	54.46
2000	54.54
2001	54.66
2002	54.69
2003	54.83
2004	55.02
2005	55.22
2006	56.13
2007	57.11
2008	57.91
2009	58.31
2010	59.88
2011	61.48
2012	62.88
2013	62.91
2014	62.9
2015	62.88
2016	62.9
2017	62.91
2018	62.83
2019	62.73
2020	59.54