Year	Percent
1991	59.62
1992	55.06
1993	51.47
1994	50.67
1995	49.66
1996	49.96
1997	51
1998	52.14
1999	53.7
2000	54.23
2001	54.92
2002	54.92
2003	54.64
2004	54.28
2005	55.52
2006	56.32
2007	57.1
2008	57.6
2009	55.45
2010	54.82
2011	55.17
2012	55.08
2013	54.22
2014	53.78
2015	53.33
2016	53.32
2017	53.66
2018	54.94
2019	55.31
2020	54.78