Year	Percent
1990	61.58
1991	61.54
1992	61.47
1993	61.36
1994	61.22
1995	61.03
1996	60.72
1997	60.35
1998	59.93
1999	59.48
2000	59.03
2001	58.69
2002	58.37
2003	58.07
2004	57.82
2005	57.63
2006	57.8
2007	57.99
2008	58.2
2009	58.4
2010	58.6
2011	58.87
2012	59.19
2013	59.51
2014	59.77
2015	59.94
2016	60.06
2017	60.12
2018	60.29
2019	60.38
2020	57.04