Year	Percent
1991	55.69
1992	56.07
1993	56.4
1994	57.46
1995	58.2
1996	59
1997	59.13
1998	59.23
1999	59.12
2000	59.02
2001	59
2002	59.08
2003	60.16
2004	61.2
2005	62.17
2006	62.02
2007	61.69
2008	61.57
2009	60.95
2010	59.95
2011	59.46
2012	59.99
2013	60.69
2014	61.09
2015	60.4
2016	59.31
2017	58.89
2018	58.47
2019	58.06
2020	53.09