Year	Percent
1991	60.64
1992	60.43
1993	60.73
1994	61.66
1995	62.11
1996	62.4
1997	63.01
1998	63.31
1999	63.56
2000	63.77
2001	62.92
2002	61.9
2003	61.39
2004	61.43
2005	61.74
2006	62.14
2007	61.97
2008	61.21
2009	58.36
2010	57.45
2011	57.36
2012	57.96
2013	57.89
2014	58.36
2015	58.73
2016	59.13
2017	59.58
2018	59.89
2019	60.27
2020	56.31