Year	Percent
1990	58.3
1991	58.06
1992	57.93
1993	58.07
1994	59.01
1995	59.63
1996	59.03
1997	58.19
1998	57.27
1999	56.24
2000	56.98
2001	55.98
2002	55.75
2003	55.52
2004	55.26
2005	55.12
2006	54.99
2007	54.91
2008	54.89
2009	54.96
2010	55.03
2011	55.29
2012	55
2013	55.66
2014	54.44
2015	54.76
2016	54.56
2017	54.52
2018	54.35
2019	54.16
2020	52.49