Year	Percent
1991	56.21
1992	56.16
1993	56.23
1994	55.85
1995	55.59
1996	55.32
1997	55.01
1998	55
1999	54.94
2000	55.02
2001	55.15
2002	55.2
2003	55.24
2004	55.45
2005	55.77
2006	56.05
2007	56.7
2008	57.2
2009	57.51
2010	57.84
2011	58.16
2012	58.16
2013	58.12
2014	58.06
2015	57.97
2016	57.44
2017	56.88
2018	56.8
2019	56.69
2020	54.99