Year	Percent
1991	56.87
1992	55.71
1993	54.86
1994	55.11
1995	55.54
1996	55.88
1997	56.73
1998	57.16
1999	57.55
2000	58.03
2001	58.13
2002	58.17
2003	58.42
2004	58.59
2005	58.82
2006	58.77
2007	58.68
2008	58.72
2009	57.37
2010	57.05
2011	56.83
2012	57.15
2013	57.53
2014	58.5
2015	59.06
2016	59.51
2017	59.81
2018	60.24
2019	60.61
2020	60.05