Year	Percent
1991	61.43
1992	61.47
1993	61.42
1994	61.38
1995	61.31
1996	61.34
1997	61.33
1998	61.3
1999	61.2
2000	61.11
2001	61.12
2002	61.01
2003	60.94
2004	60.84
2005	60.71
2006	60.74
2007	60.67
2008	60.58
2009	60.38
2010	60.2
2011	60.08
2012	59.94
2013	59.8
2014	59.7
2015	59.58
2016	59.33
2017	59.11
2018	58.98
2019	58.85
2020	56.98