Year	Percent
1991	56.54
1992	56.49
1993	56.45
1994	56.44
1995	56.45
1996	56.36
1997	56.21
1998	56.06
1999	55.9
2000	55.76
2001	55.53
2002	55.27
2003	55.04
2004	55.02
2005	55.01
2006	55.28
2007	54.99
2008	54.66
2009	54.16
2010	54.99
2011	54.74
2012	54.48
2013	54.22
2014	54.2
2015	54.16
2016	54.13
2017	56.29
2018	56.48
2019	56.62
2020	52.77