Year	Percent
1991	61.77
1992	62.14
1993	61.24
1994	60.21
1995	60.13
1996	58.32
1997	58.09
1998	56.46
1999	56.36
2000	57.09
2001	57.74
2002	58.29
2003	58.84
2004	59.19
2005	59.57
2006	59.92
2007	60.11
2008	59.87
2009	59.6
2010	59.29
2011	59.48
2012	59.46
2013	59.36
2014	59.16
2015	58.97
2016	58.87
2017	58.47
2018	58.39
2019	58.25
2020	55.75