Year	Percent
1990	58.02
1991	57.62
1992	57.11
1993	56.59
1994	56.06
1995	55.52
1996	55.07
1997	54.67
1998	54.29
1999	53.95
2000	53.65
2001	53.29
2002	52.29
2003	52.33
2004	53.49
2005	53.3
2006	52.72
2007	53.11
2008	53.29
2009	53.27
2010	52.68
2011	51.81
2012	51.28
2013	50.67
2014	52.14
2015	52.54
2016	51.19
2017	51.61
2018	51.36
2019	51.48
2020	51.33