Year	Percent
1991	60.02
1992	59.88
1993	59.51
1994	59.69
1995	59.84
1996	60.09
1997	60.05
1998	59.9
1999	59.71
2000	59.86
2001	59.46
2002	59.32
2003	59.1
2004	59.02
2005	58.98
2006	58.92
2007	58.83
2008	58.21
2009	58.23
2010	58.41
2011	59.7
2012	60.7
2013	62.07
2014	62.44
2015	62.46
2016	62.1
2017	62.2
2018	62.64
2019	62.59
2020	61.27