Year	Percent
1991	58.68
1992	57.35
1993	54.28
1994	52.09
1995	49.53
1996	45.29
1997	49.16
1998	50.66
1999	51.25
2000	52
2001	52.72
2002	53.4
2003	54.12
2004	54.89
2005	55.72
2006	56.51
2007	57.33
2008	58.13
2009	58.77
2010	59.17
2011	59.51
2012	59.81
2013	60.06
2014	60.3
2015	60.46
2016	60.62
2017	60.79
2018	61.46
2019	61.04
2020	59.79