Year	Percent
1990	56.52
1991	56.47
1992	56.46
1993	56.38
1994	56.25
1995	56.09
1996	55.9
1997	55.73
1998	55.61
1999	55.48
2000	55.36
2001	55.26
2002	55.16
2003	55.12
2004	55.11
2005	55.16
2006	55.21
2007	55.33
2008	55.55
2009	53.94
2010	52.48
2011	52.54
2012	53.04
2013	53.73
2014	54.05
2015	55.38
2016	55.52
2017	56.18
2018	55.99
2019	56.08
2020	51.49