Year	Percent
1991	62.55
1992	61.51
1993	60.93
1994	60.72
1995	59.96
1996	59.85
1997	59.97
1998	58.5
1999	57.45
2000	58.26
2001	58.13
2002	57.11
2003	56.43
2004	57.05
2005	57.53
2006	57.93
2007	58.43
2008	58.24
2009	57.1
2010	56.6
2011	57.58
2012	58.11
2013	58.78
2014	58.67
2015	58.75
2016	58.59
2017	58.67
2018	58.52
2019	58.1
2020	54.9